I.,
I have both the CLassic and the Mega Reverb, running on a Powercore. We also have a Lexicon 480, 224, 90, an old AKG 68K and a BX20. I have also heard the System 6000, the M5000 and the Lexicon 300. I can tell you that none of the plugins do the job for me. Sometimes I find Reverb One (shitidesign) and the Platinum Reverb in LOGIC useful. Generally, when using the Classic and/or MegaReverb I get better results when I process (freeze) tracks with reverb and then add them as soundfiles to the preexisting (unprocessed) tracks. Perhaps a jitter/timing and or resolution issue? The IR reverb in SEQUOIA I use quite a bit for postproduction, more than any of the other reverb plugins. For some reason the reverb always sounds better in post processing as opposed to real-time. But the truth is that in most cases I prefer the larger Lexicons in direct comparisons. It really is all about the algorithms, and less about the actual hardware implementation. I suppose David Griesinger really does know his stuff. And yes, I do work in 96 K most of the time, yet run the Lexicon analog in/out through some auxes. No problem here, except that it is time consuming because it has to be done in real-time. For classical music when time and money permits I usually retrack things in various halls. Expensive, but worth it.
Cheers
P.S.: For your groundloop problems I would recommend looking into getting a balanced powersupply. Dropped 7dB in noisefloor in our room!