[Steve DeRosa]

In order:

• Sounds like you're a real Ampeg guy at heart as well as a mod junkie, and I'd recommend searching out and playing some good original blue-check amps from the '63-67 period (if you haven't already done so) - find out first-hand what the buzz is all about, and use those as your tone model...
• Since you seem to know something about amps I'll assume either you or your tech checked to see that everything is in order, particularly in terms of power tube bias (don't recall if the reissue Jets were cathode/fixed/variable bias) - that said, JJ's aren't my favorites when it comes to either tone or longevity; FYI the Preferred Series tubes are NOS pre-Glasnost Soviet mil-spec issue, I use them in both my Bugeras - six years in the V22 with no signs of quitting - and if they were good enough for Andropov and Gorbachev to use in their MIG fighter-jets, they're more than good enough for your Jet...
• "Enough bass" is a subjective judgment that only you can make - suffice it to say that TNO's assessment is accurate to my ears, so if you like the "tight" low end of the C-Series Jensens you'll probably be a happy man; if you need something "bigger" sounding with less breakup there's the Cannabis Rex or (my fave) Swamp Thang (FYI the Black Powder is discontinued), which raises the issue of clearance - I'd go to the Eminence website and listen (with some good headphones) to the sound samples to help narrow down your choices, which leads me to:
• If you want to squeeze more volume (as well as tone) out of your 15-watter as quickly and painlessly as possible, look for the most efficient (dB/W/M) speaker you can find that meets your tonal requirements (and fits in your cabinet) - refer to my prior comments about the Swamp Thang, and keep in mind that we're talking about a 22W 1x12" (think Deluxe Reverb) that'll keep pace with two of the more powerful production combos out there; your needs and tonal Holy Grail may (and probably do) vary, but the principles are the same - I have no doubt that your signature sound is out there, and for less money/time/effort than you think...

Enjoy the search, and good luck...