Regarding the SIAB, IMHO anything that runs a tube at low voltage (<200V) is not going to sound satisfying. That being said I built one from scratch (no kit) and was pleased with the sound. Seems to me it's more of a studio tool, into an amp it was just so-so, into a mixer with some FX it was way better (used it with Cubase for years until I finally got Amplitube.)
Regarding the Quadrafuzz, it has great sounds in it but it takes a LOT of fiddling with the knobs to get there. This runs counter to many guitarist's thinking, which is why the TS-9 is so popular IMHO: it sounds good (maybe even great) but any knob position works. With the Quadrafuzz, I found the biggest weakness to be the lack of presets... it takes you a long time to find a nice sound (not only fiddling the knobs on the QF but on you amp as well), then you either have to write down the knob positions or try to remember them (impossible!) Interestingly enough this was "fixed" with the plug-in VST version (which sounds the same and better). I would start by distorting the high end only, then working your way down, adjusting the volume of your guitar and/or any other FX before the QF since it seems to be sensitive to levels.