Tube amps that kick ass?

Kora Kosmos or Kora Titan Monoblocks

I think of the rock bass you are looking for is actually frequencies above the subwoofers in the 5A, a lot of apparent bass is above 30Hz so you still do need a good tube for rockin bass. The best bass I have heard from a tube amp was the CAT JL2 - though the Atma-sphere with the right speakers does produce really good bass, I don't Vandersteen is the right speaker though.

cayin or vas. you need to hear to believe.

Sonic Frontiers Power 3 can be had for <$3500 if you can find them, they are very good for the money.

BAT 150SE is superb if 150 wpc is sufficient, BAT has tremendous drive and speed that sounds more powerful than 150 wpc. you can start with 75SE and upgrade to 150SE if you like the sound, you gain more than power when you bridge. BAT can be further upgraded with some aftermarket parts, there are a few threads on audiogon discussing this topic and result is well worth the price.

Canary CA-160 monoblocks, 140 wpc. I second their recommendation that was made to previously. I just bought a pair off Audiogon and to say the least I am very impressed.

They really spank my Von Schweikert VR 4 JR's. The sound is excellent. Very good taut bass, a wonderful mid range, and clean highs. These amps have "it". You just want to listen to them as they are so engaging, smooth, and textured. I use Canary monblock preamps to drive them.