I recently went through an amplifier upgrade quest and ended up falling in love with the sound of Theta Digital amps. A 2-channel Dreadnaught II would fit into your budget, although on the preamp side, Theta is apparently more geared towards multi-channel pres (though you can get a Casa Nova for a song, nowadays). However, given your comments about bass and wanting a rich sound, you may want to audition some Krell amps and preamps. Make sure that you check out the FPB series amps. Krell makes some pretty killer preamps, too. If you go Krell, we're definitely talking used market.
Tom.
Tom.