Yep, I found R8 to be a nice pairing with Mason FS. R8 was pretty reference in signature, but not a thin sound and notes had weight to them. I thought it worked well. My preferred pairing is always my desktop setup (Ifi iDSD Pro) on tube mode, but recently I got the SP2k and N6ii Ti. I guess I'm not very helpful in saying that they've all been great with Mason FS. It's a difficult IEM to drive, so noise isn't an issue with most sources. Each DAP/DAC changes the synergy a bit, but I haven't come across anything bad per se. My S1 dongle even sounded okay, but a little less life and character given the power deficiencies.
As for genres, well, it's not a bass monster so I don't use it for EDM as
@aaf evo said. To me, where it shines is in band-based music and vocal-centric stuff. It's a very natural and highly-detailed sound. I prefer it to Traillii (just had to throw that out there to set the internet on fire).
Also, worth noting, I absolutely LOVE it with the Eletech Aeneid cable. Comfort, for me, is highly improved over the stock cable. I suppose I could have saved $2 grand and just got the FuSang without the Attila in that sense
-Collin-