Would an amp or preamp have a larger SQ increase?

I have a modest system right now consisting of a Carver HTR-742 as a preamp, Adcom GFA-545, and Ascend Sierra-1's.

I recently replaced a pair of B&W 601S1's with the Sierra's, and it was a large improvement. I'd like to upgrade my amp and/or preamp (eventually both), but was wondering which I should upgrade first to give me the larger increase in SQ? I was hoping to stay in the $6-700 or less range for each component.

Only real caveat is that the preamp has to have a remote. We listen to Blues, light Jazz, as well as electronic music more oriented towards Ambient and Dub. Also sometimes rock/pop from the 80's-90's.

I do a lot of my listening after our 2 small kids have gone to bed, and my listening room opens up to a stairway with the bedrooms upstairs, so I'd like an amp/preamp that sound good at lower volumes.

I've been doing a lot of reading on equipment, but since I haven't been able to listen to them it's hard to make a decision. I *think* I want a SS preamp since I like electronic music and want the bass nice and tight, as well as deep and controlled. But, maybe what I really want is just all around quality in my sound? I'm not hi-fi educated enough to know :-(

Some equipment I think I'd like that may be in my price range is:

Musical Fidelity A3.2CR or A308CR and Parasound HCA-2200 mkii.

Thanks for any comments,

Mike