Bass is the one thing that makes me hesitant about tube amps. I do use subwoofers, so I guess I really should not have a concern because I can always adjust it to make up for what I feel is missing on the low end.The amp I play has full power bandwidth to 2Hz and my speakers go right to 20Hz (the woofers have a free air resonance at 22Hz). I've had solid state amps on these speakers (Classic Audio Loudspeakers T-3) and they just don't play bass as well. Less impact, less definition.
But that has a lot to do with how the amps and speakers play together. The CARs were designed to be easy on tubes and so are 16 ohms. Transistors have trouble making power into impedances like that (although the flip side is they have less distortion too and so sound smoother).
IMO rather than changing out the amps in the OP, a better move might be to get a speaker that is friendlier to tubes. There is no point (from the standpoint of an amplifier designer) to make the amp work hard regardless of what kind of amp you have. The easier the amp has it, the less distortion, the less distortion the smoother and more detailed.