Hi, michaelmickj7,
You mention that you needed more bass? Or do you find that the sound does not have enough weight?
the overall tonality of the sound is pretty much determined by the speaker, I am afraid. The electronics can improve things like the clarity in each respective frequency range: lows, mid, and HF, but cannot really change very much the overall sound.
Adding tubes is opening another whole new variable unless you have got the basics right first. It does add a lot of warmth and lushnes to it but has their own set of problems if not matched probably.
If the speaker already producing a nice deep weighted sound, then by improving the quality of the electronics you can make the highs clearer, smoother, the bass clearer, more defined etc but the overall sound is still pretty much in the same ballpark.
I concur that you must get the speaker right first, and then slowly match the amp to the speaker.
i have a pair of Harbeth (Super HL5) and I love the beautiful and clear midrange with well integrated bass and smooth highs. When I upgraded from a Stratos plus to MONO extreme, I basically got the same sound, but just a whole veil lifted, ie, much better defined bass, clarity in all ranges, and extended HF etc etc, so it sounded like day and night on one hand, but the overall tonality did not change much. But if you put in another speaker, then I am sure the sound will change by a lot.
Hope that helps:)