Never heard e30, so can't say much about it.
Based on many amps I tried, I don't think A90 lean on bright/cold side though. It's kind of neutral with slight warm character.
Even though A90 produce excellent micro detail, I agree that this amp is not produce the most musical or high energy kind of sound, and may reveal some "dull" bite on mid to treble area. Of course impression come with my current set up Chord Qutest and ZMF Verite, ymmv.
Sundara itself, personally, a little bit harsh and there are some peaks at upper mid to treble area.