I am so surprised no one is biting on this, I am about to start the biamp process with my 3.6 Magnepans, and I plan on using many amplifiers to see which is best... and use the best ones to get the job done... Searching for that sound!
I have an active Electrovoice EX-23 crossover (70$ junker) that I may check the specs on, and see if it mates well with the Magnepans, or I will possibly throw that one on the 'bay and check out the Audio Research one, or perhaps a Bryston. Magnepans have specific crossover needs, as detailed in the owners manual... Make sure what you have, and how you set it, corresponds with the manual!
Amps I have include DIY Icepower 1000w monos, a Van Alstine Fet Valve 500hc, and a NAD 208thx which is really good in the bass department. I am currently looking for some large vtl monos, like MB 450's or 750's...