It was the MPX 550. They don't make it anymore, but it was basically their top of the line processor. Well worth either finding a used one of those, or getting the new equivalent.
Unfortunately I haven't had it in years. I just remember really liking it and that it was a good quality unit. I am sure it would work fine- Lexicon is really good stuff. I believe it is line level.
Check ebay for a Lexicon MPX G2. It's a great processor, as many here would agree with. It also was designed specifically for guitar. You can get effects both in front of, and in the loop of your amp. Well worth the investment. Usually you can find them for at or around $400.
Unfortunately I haven't had it in years. I just remember really liking it and that it was a good quality unit. I am sure it would work fine- Lexicon is really good stuff. I believe it is line level.
The two Eventides that are in my signature are really nice, and can be switched between line and amp level.
They sound really good, but they are complicated- They are very flexible with a lot of options. For example, I have finally figured out how to get a good wah sound out of the ModFactor, so I don't need a wah pedal. I like complexity, but not everyone does. They are also floor pedals, not rack. still they are definitely studio quality- No problem recommending them!