Arthur,
There are a lot of different 300B amps out there that sound better, to me, than the Sophia, but, decent amps are somewhat costly because they employ quite expensive output transformers.
Among the most common low-powered triode tube types--the 300B, 2a3, and the 45, I personally like the sound of the 45. The 45 has tighter and more punchy bass than the 300B (by comparison, the 300B tends to be flabby and a bit overblown in the upper bass, lower midrange), and is not as lean sounding as the 2a3 (sort of in the middle between the two others); the downside being it delivers even less power than the 2a3.
It sounds like you are looking for a range of different sounds from your collection of amps. A pushpull EL34 amp would certainly be a good candidate. If the chosen amp can run other tubes in that family of tubes, I personally like 6L6 tubes for the sound even though they do not put out as much power. There are some other rare tube types that sound fantastic in pushpull amps, like the 349, 271 and the extremely rare 252.
Another completely different area to explore are output transformerless amps. This type of amp tends to be extremely lively and dynamic sounding.
