Like you, I really like my 300b SET amp. It presents in a way that SS, push-pull, or parallel amps can’t. I also don’t listen loudly and describe myself as a micro, not a macro listener. Depth, separation, and inner delicacy are important. However, I keep a high watt SS A/B amp around for rock music. Over time I use it less and less. The ears just don’t like slam anymore.
I had Daedalus Apollo 11 speakers. Excellent and versatile. I used many different amps ranging from 1.5 watt 45 SET to 200 watt SS. 1.5 watts didn’t work on anything but girl guitar material. 3.5 watts 2a3 SET was better, but just didn’t have punch. 8 watt 300b was the first acceptable level of SET power. Bass definition and volume would be ok most of the time, even on more casual rock, but it just doesn’t snap down low like a class A/B amp can - either SS or tube. I tried 20 watt GM 70 SET and 30 watt 845 SET. Each had ample low end heft, but still didn’t snap. Their compromises in inner detail rendered them unacceptable to me.
Perhaps the best compromise amp I used with the Apollo’s was a VAC 200iq (push-pull KT88). It could hit hard with voluminous bass and had tube harmonics and long decay. A Thomas Mayer on hand proved to have superior sound quality overall (more refinement and coherence). Just can’t find everything in one amp it seems.
Alternately, if you are committed to the 300b amps, there are other speakers to consider - DeVore, Audio Note, or Tobian could work well. I ended with Tobian.
A compromise of another kind could be Daedalus with the Spatial Audio Blackbird monos - 300b push-pull by Dan Sachs and Lynn Olson. I may try these myself.
Circling back, if I could only own one amp, it would be the 300b SET. As always, many paths are possible.