I recently bought the Hsu VTF2.3 -- works very well with the axioms I have (M60, vp100, QS4). I was surprised at how much difference it makes -- even with the M60s. They have some smaller units that might be more suitable for an under desktop scenario.

AV equipment (in case you care)Panasonic TH-50PE700U,PS3 80GB,HK 445,Axiom M60,QS4,VP100,Hsu VTF2.3