I would describe A90 as a very high SQ amp but plain, everything is there but doesn't make you feel anything at all, like a food you really like without salt, flavourless. I also have the A30 with 2x Burson V6 Vivid and I also prefer it over the A90.
Meanwhile the Valhalla 2 which I think I prefer it over Jotunheim 2, at least with the Focal Clear: I get everything I like, I can't stop listening to music with it. The instruments, sounds, effects, everything coming from different places and corners in space, very holographic and pleasant. Plus I never get any kind of fatigue.
And finally the Jotunheim 2, with Arya: They are a very good couple, I usually listen to videogames music: Final Fantasy, jazz, classical etc and percussion, wind and strings has lot of texture and weight... I don't miss anything when using the Jotunheim 2 and If I want that little extra spicy just turn up the gain switch and lows become very impactful and aggresive.
I would really like to try the Singxer SA-1 but so far I'm very happy with my current setup.