Don't get the rampage board, the WS SAGE/10 is confirmed to work well
Just don't upgrade to 1102 BIOS, stick to 0905.
Cheapest I found in the US is at
SuperBiiz.
But if you do want to experiment with RAMPAGE go for it. I personally am tired of swapping X299 boards haha
This one you linked should work well (technically its 2 ports per header, so 4 ports). As long as it's not a Fresco Logic, it should be ok. On
Silverstone's website it says macOS is natively supported.
Yeah I tried this from 2 different brands, it did not work at all. On another forum someone confirmed if you make a custom one yourself it should work (making sure you follow proper pin-outs that is). But I'm too lazy for that. Technically that USB-C header on the SAGE/10G is a ASMedia ASM1142,
same as the other card I posted. But for some reason this adapter doesn't work properly.
You might try
this card and
2x of these adapters for 2 internal headers. Remember, each of the USB3.0 headers on either your motherboard or these cards are considered 2 ports per header, so technically you have 4 internal headers.
A single internal USB3.0 header is 2 USB3.0 ports (Or 2 2.0 ports, or a combination of both). But to split a single header into 2, you need some kind of adapter. I
tried this and it didn't work at all.
Something like this might work, just haven't tried.