Just an amp or an integrated?

I have a pair of Vandersteen 2Ci's that I've been running with Acurus separates for a while now (the RL11 and a150). My main digital source is an Asus Xonar Essence ST soundcard.

I read in another forum post here that often you can obtain immediate sonic improvement if you remove your preamp from the signal path, so I now have my Xonar ST running straight to the a150 power amp, since I have a volume control on the sound card. Is this ok to do? And if so, I think I'd like to replace the a150 with a better quality amp. Any recommendations on an amp around $1,200 or under, or should I be looking for an integrated to do this job?
If you could swing about $500 more, there is a Butler TDB-2250 here on A'gon that would be a KILLER amp for your speakers. The owner of the amp has also driven Vandersteens with his amp and liked the combo. Read up on this amp, it is truly a fantatsic piece of engineering...

For the record, I have a Butler TDB-5150 driving my home theater/stereo system and it sounds glorious...