Want More Bass

Get a sub, dude, and be happy.

Sub..VMPS Larger Subwoofer will solve your problems I think..

If you just changed amps, & are now bass-thin, isn't the problem obvious? Your speakers are obviously up to the task; they were working fine previously weren't they?
But if you're really stuck on keeping that amp, then try tweaking it. Tube roll. Try out different upgrade AC cords. Try different interconnects / speaker cables, for better synergy. Try shelving, cones, pucks, footers, & etc.
But forget the subwoofer!

Bob, I think your right about forgetting the sub woofer but for a different reason. One of his statements, that no one has keyed on, is his preference for low volume sound. One of the ancient studies about human hearing shows that we tend not to hear the presence of low frequencies at low volumes to the same degree that we hear the mid-range/highs. For a long time recievers and intergrated's included a tone contour control which implimented the Fletcher Munson curve (which has since been somewhat discredited - I believe because of the high end emphasis, not the low end). This provided for a increase in the bass which automatically diminished (the added emphasis) as the volume was increased until you had a flat frequency response signal at the output.

As I see it, if the poster adds a sub and tunes it for typical low volumes he'll be very unhappy when he increases the volume as the sub will then become overbearing. I'm not sure that full range speakers will make that much difference, but there are some full range speakers that do present a more balanced and resolved sound at lower volumes, however his room placements might make implementing full range speakers somewhat problematic.

Newbee,
I want to add to your thought about low volume listening and the KEY point in this case turs the AMP and the AMP only. Less-likely speakers are not rated conservatively and I feel the case is that speakers now don't even rich 65Hz and starve for more power.