Well, after receiving timv's blessing, I gave it another shot and my amp worked fine for over an hour of very loud usage.
Once again, I connected my bass to an A/B/Y pedals center input with its (ch-A) output connected directly to my SVT-II normal input.
The (A/B/Y) pedals channel-B output was connected through a fuzz pedal and then into the amps secondary (front-mounted) "Bright input" jack.
By foot-switching my A/Y/B pedal, I can now alternate between 3 distinctly different tones:
A = Normal input (clean only)
B = Bright input (fuzz-only)
Y = Both inputs (a clean/fuzz-bass blend)
I started out in mode B, set my distortion pedal for a medium fuzz tone and started playing, when I clicked my ABY box to run both channels simultaneously, the bright channels (fuzz-tone) remained unchanged, but I was rewarded with the distinctly-audible addition of my normal clean bass tone.
Switching back to ch-A eliminated the fuzz and brought me back to just clean.
Switching to ch-B produced the fuzz-tone, but the sound was thin and hollow, and definitely was lacking in low-bass frequency's. (at least with my fuzz-pedal and settings)
All these transitions were smooth sounding and without any sudden pops clicks or volume swings.
(note: my fuzz pedal does have a separate volume-level knob, which is a very handy feature for this particular connection scenario)
Again I only played it for a hour or so, but this amps dual-front inputs do seem to blend these two signals very well.
It sounded really great and does indeed seem to be working fine on my SVT-II now. I'm not sure how often I'll be using this arrangement but I definitely prefer it to simply installing a fuzz pedal in the normal (in-line) manner because the clean fundamental sound can still be very present even with an excessively distorted tone blended in.
I really liked it and think you guys should definitely give it a try if your unsatisfied with your prior results using distortion type pedals with this amp.
