I am in the same boat with you. Well I bought the direct-die kit and ordered the MB-X VRM for the Apex. In Watercool's German site it says that "optically"/"optisch" the VRM block should fit the Extreme too. I hope so, I guess even older blocks from previous Rampage boards could fit because when I've swapped Rampage boards from X79 to X99 to X299, those are almost like copies from each other.

Another thing is that you need to cool the Aquantia 10G chip, I went extreme and ordered a monoblock from another brand and they supply a heatsink for the 10G chip, I can take advantage of the monoblock with my Apex build if I want and use a standard CPU block+VRM block + passive 10G heatsink with the Extreme.

Yeah it would be great if Watercool had a passive heatsink for the 10G chip and could verify that the block fits the Extreme too. Also I would like to buy their Heatkiller IV CPU block but I am unsure if it makes proper contact with the direct die unless I use the standoffs, screws and springs from another block? I guess I'll ask der8auer in YouTube if he could try that block.

If I get my order from Watercool someday, I'll try to remember to report here how it went. Is this the third or fourth business day and my order still hasn't shipped.

Hey guys,
we are currently trying to find this exact information, too. We are 95% sure that the R6 APEX blocks will also fit on the R6 Extreme, but wanted to find final confirmation before officially announcing it.
Xarot, please check your emails, I'd love to hear your experience with this block!

If it is compatible (as expected), we will also bundle a passive heatsink for the Anquantia chip with every order of the R6 blocks.

Regarding mounting on Der8auers Direct Die Frame: in his german reveal video, he explicitly confirmed compatibility of our Heatkiller CPU water blocks with his frame. So this should be no problem. If any of you should try this, we'd also be highly interested in temp results!

The VRM block itself is a perfect fit:

i.imgur.com/mLlEMgD.jpg
i.imgur.com/xI61QnQ.jpg
i.imgur.com/RHbKIqQ.jpg
i.imgur.com/ZZFq0O0.jpg
i.imgur.com/tgxiKWz.jpg
i.imgur.com/80VXZN3.jpg
i.imgur.com/7QSe7tF.jpg
i.imgur.com/YgPtBt7.png

Thanks again for testing and the pics! Highly appreciated