First, what is it that you think is missing/lacking, or can be inproved in your system? Does your system not sound dynamically transparent or powerful enough, that you're looking for more assistance? You could try doing the biamping of those speakers. I think you'd find it stronger and more dynamic. However, you don't need to waste money on buying a second Levinson to accomplish this!!! YOu should consider buying something like a less expensive, yet extremely dynamic and bass strong, Parasound amp to do the bass Dubties on the bottom posts of your Revels! The Parasound HCA3500 is dirt cheap used, and has mondo bass authority and control, and will handle the woofers on your Revel's nicely!..it won't touch the midrange really, and you can let your levinson take care of the midrange on up!!!
The Parasound also has volume controls to allow you to level match! IT also has XLR connections too.
Overall, you'll have a much stronger dynamic, with more weight and authority by byamping on those speaekers I think. You should be ok overall, as this speaker probably is crossed over low enough between the posts to keep a proper balance of timber, etc. Sometimes you have a brightness/forward sounding imbalance issue in the crossover when you biamp speakers such as "two way" monitors, or speakers crossed over too high at the binding posts from one another. But you should be good with yours.
As for the extra woofers, unless you're doing HT, heavy dubty pipeorgan demo's, and are willing to EQ the woofers youre considering adding, and spend lots of time setting em up for flat frequency response (location is the most important with ALL speakers), you'll only slow down the sound of you're system probably, and muddy things up..IMO.
Also, with Biamping, when done properly, if your speakers are in a less than ideal location sonically, or in a smaller difficult room, and your bass response is less than flat/stellar, you could also get an EQ in between the bottom amp and the speaker posts for the bass woofers! A good Parametric, or better yet, digital parametric EQ, will allow you to tweek the bass to perfection (after good speaker set-up of course), and not sacrifice the integrity of the midrane or treble!...very convenient. If however you have the speakers set-up very well, and are getting pretty good semblance of "flat" frequency response throughout, you don't need to mess with this. (actually most people should spend much much more time with proper speaker/seating set-up/location).
The only other thing I would probably add would be perhaps trying a good tube preamp in your system, for some added tube magic if your system needs it...it's alway's worth trying this I think.
Anyway, good luck, and perhaps you could fill in a little more on you're needs/desire/challenges with the system thus far?
