I have been doing some serious ABX testing between A90 and THX 789 using D90 and LCD-4 for the past week.
Very first thing I noticed was a90 seemed little warmer but upon further listening i hear that it has more clarity in mids and much better sub bass compared to THX. But it takes a hit on upper notes, it lacks air on top. The overall synergy is of more details on individual instruments; but as the tracks gets busy, the soundstage, imagine and separation takes a hit.
It degrades the holographic nature compared to THX, which is the whole game-plan/aim of my setup with LCD4 and d90. It feels more musical but lacks the 3D nature which makes the headphones disappear. I always felt that I am wearing the headphones even after 15-20 minutes of listening.
Upon further research i found that on paper, a90 has much better slew rates but much worse crosstalk between channels.
This confirms my findings that a90 sufferers in separation and soundstage which ultimately ruins the “in the room” holographic sound.
THX on the other hand feels so effortless even with less sub bass impact and individual instrument details. Just because it maintains that Impressive spatial separation and room size clues, no matter how busy the track gets.
I really wanted to like A90 to pair with d90 in terms of sound and looks. I tried really hard to like it but I just couldn’t ruin the main objective of my setup. So sadly I am returning it and keeping my old faithful THX 789.