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@ Wootz: what i take away from this YouTube clip is your dedication in what you're doing.
And i think i'm not the only one.

Update on the Takamura R2 210 Gyuto:

According to the Chef this edge done on Paper Wheels lasted him 2 months in his commercial kitchen, which was just as long as the factory edge had lasted him.
During that time he sometimes touched up the edge by stropping it on an MDF strop with 1.0 micron diamond compound until that no longer worked satisfactory (in the last week or so), after which he used a fine ceramic rod on it.
Differences with the factory edge were that the Paper Wheel edge had a slightly smaller edge angle (+/- 20 degrees inclusive instead of +/- 22,5 degrees inclusive), was finer polished, and had a higher sharpness.

We're still in the process of finetuning the edge to his specific requirements, and next time he brings in the knife it will probably get a little less refined edge to see if it's useful life can be prolonged a bit more.
In his kitchen the real edge killers are the mandatory plastic cutting boards which are very abrasive on knife edges, together with the almost unavoidable tiny sand particles which sometimes remain in the huge quantities of vegetables that need to be processed.

With this knife i actually forgot to tape the surface of the jig, normally i use a piece of packing tape on it.
I never tape the blade itself.
BTW: maybe i've found something better than packing tape, still have to try it.

This is a customer's knife, and i don't know if he wants a sharpening notch.

The blade on this knife has not been thinned,

This user Spyderco Resilience was done on my version of the small platform jig.
In the pics there is still a bit of burring at the heel, which is also the tricky part to sharpen on this model with the small platform jig, because of the non-existing ricasso at that point in combination with the slightly protruding handle.
I had to use the edge of the stone (an SB-250 Blackstone) to get there at all, and as you can see it's not visually perfect.
After sharpening it was deburred freehand on the Tormek leather wheel.
The new edge measures an almost exact 30 degrees inclusive and the apex is keen enough to whittle one of my chest hairs from root-to-tip at 3 centimeters from the point of holding.

Do you know the steel type and hardness of your knife ?

Carborundum = Silicon Carbide

Haven't sharpened CPM REX121 steel yet, but your CBN will certainly grind it as it is much harder than both the steel matrix as well as all it's alloying elements.
For deburring however i would definitely also use fine CBN (or diamond) compounds to cut through the large amount of vanadium carbides, which will provide for the best possible edge that will also last the longest.
PA-70 being aluminium oxide is literally unable to cut through vanadium carbides.

Also keep in mind that there are many different qualities of ceramic knives, just as there are with steel knives.
Cheapies in general aren't worth it to resharpen them, best to tell the owner to simply buy a new one.
I've stopped sharpening these category completely.

Even the two best edge takers & holders among ceramic knives i've encountered thus far (Forever and Kyocera) differ quite a bit.
With an SB stone you can easily grind Forever ceramic knives to repair & set completely new edge bevels, while the same stone takes a lot more time on Kyocera knives.
For those i'm sure a CBN or diamond wheel would work faster and probably better, but currently i don own one.
After grinding you have to polish the bevels, both to get the sharpest apex as well as the best edge holding.
Toothy edges are a no-no on ceramic knives.
Imo the Forever knives do a bit better in the edge holding department than Kyocera knives as the material seems more resilient/tougher, it chips less in use, and when it does chip those chips are noticeably smaller.

This is how i do it:

https://www.bladeforums.com/threads/forever-sc-16wb-ceramic-knife.1206014/

https://www.bladeforums.com/threads/sharpening-a-black-ceramic-kitchen-knife.1088417/#post-12446725

Around half an hour, also due to the visual inspections in between passes and sharpness tests afterwards.

The owner of the Takamura R2 just sent me the link to this clip, in which he uses a grape to test the new edge:

https://m.youtube.com/watch?v=ID9KZW0d9ss&ebc=ANyPxKoyX72SsCjqu911cdH_dCkEw68tPNE8oUCSzdcOran-LlZb1WqXiuKv1H4EA5q0nOhue4ImgsX__7quwMf7REhAJl26rg

On this knife the Tormek was not used for the actual sharpening of the edge, but in a very important supporting role.

Right hand Takamura R2 Gyuto 210 mm from a local Chef, who got it as a birthday present from his wife.
The knife has already been used for two months in the commercial kitchen and it was time for it's first resharpening, which i did yesterday on a Paper Wheel with 15 micron diamond compound and then deburred on a second Paper Wheel with 0.25 micron diamond compound.
The idea was to make an edge that would do both slicing & pushcutting well, and also to remove as little steel as possible from the fine and thin R2/SG2 blade @ 63-64 HRC.
The new edge measures +/- 20 degrees inclusive and can whittle a chest hair from root-to-tip at about 4 centimeters from the point of holding, and after a few test cuts into a old piece of beechwood cutting board.

I took these pics with an old Ipad and actually wanted to erase them again as being not good enough until i enlarged the last picture twice.
At first i thought i saw small dirt spots on the new bevel, but those tiny white specks were actually the sliced off peaks of the micro-dot structure on the inside of the flimsy plastic blade protector sleeve.















Total procedure:

- Repairing the point of the knife (about 2 mm was broken off) was done on the Tormek SB-250 stone by grinding the back of the blade until there was a new point.
- Flattening the old edge was also done on the Tormek (by grinding off about 1/10th of a mm on the side of the stone.
- Sharpening to burr was done exclusively on the 15 micron Paper Wheel.
- Deburring was done exclusively on the 0.25 micron Paper Wheel.
- Rounding the heel of the knife was again done on the Tormek (by grinding off a tiny bit of steel on the side of the stone.)

I've resharpened the removable blade of my sister's Felco secateur with the scissor jig, and it worked perfectly.
Very well hardened steel btw.

This is one of those home made M2 steel blades:

Imo it's not so much about the hardness of the steel matrix, as a Tormek aluminium oxide stone is harder than any steel that i know of.
Sharpening the knives you mentioned on the regular stone would be no problem, even if they had a higher hardness.

What is however important for your end results is what type of carbides are in the steel, as well as how many of them.
HAP40 is a Japanese matrix high speed steel with lots of carbide formers in it, among which vanadium which can produce vanadium carbide @ 2660 Knoop (some even claim 2800 Knoop)
There may be not many of these very hard vanadium carbides, but there are also the tungsten carbides, the molybdenum carbides, and the chromium carbides.
Next to these there is also quite a bit of cobalt in the alloy, officially to give it it's red hot hardness necessary for machining other steel, but it might also enhance the properties of certain other alloying ingredients.
Now so far i've never used a Tormek aluminium oxide stone on HAP40, but in the past i did use one for grinding a completely new edge on several home made knives from full hard M2 high speed steel (old machine hacksaw blades @ 65-66 HRC), and the results were far from optimal.
The SG-250 aluminium oxide stone would definitely grind the M2 steel (at the expense of quite a lot of aluminium oxide abrasive, the stone got visually smaller), but the final edge apex was far removed from being truly sharp and the edge that i did get was inferior.
Only when i later resharpened the edges with diamond did i get the sharpness i was looking for (hair whittling) as well as a noticeable better edge quality & longevity.

My current Tormek T7 is fitted with an SB250 Blackstone, which consists of black silicon carbide @ 2480 Knoop (another manufacturer even claims 2550 Knoop)
Hard enough for almost every type of carbide found in modern steels (except vanadium carbide), and also capable of creating an initial coarse edge on even high vanadium carbide steels like S110V steel by cutting the steel matrix and "scooping" away all those very hard (but also very tiny) vanadium & niobium carbides.
And it also does it without visible premature wear on the stone.
For burr removal or further refinement i then use diamonds, which will of course cut any type of carbide cleanly, no matter how hard they think they are.