Just tested both, i find A30 pro sounds more interesting to me, A30 pro has more punch on low frequency, a little bit smaller soundstage, but from my point of view, a30 pro is more enjoyable and more emotional, just IMHO,i will stay with d90 + a30 pro.
Tested ftom single end on beyerdynamic dt1990
Its funny i've noticed similar impressions about the a90 vs a30 from zeos, hbb, and antdroid. Something like the "a30 is less analytical, less forward". I like subjective and objective impressions but something tells me that a comment like this is made once and everyone else subconsciously picks it up. Either way I love my a30 and chose it because it was cheaper but similar performance. its great with my he6se