Classe vs Meridian vs. Theta

I think the answer probably really depends a lot on how much you value the movie reproduction, how many of the countless surround sound formats you care about, etc. The Lexicon MC-1 is widely applauded for it's ease of use and it's top-notch movie performance, but many don't think that it's top notch on music reproduction. The Proceed AVP can be had used pretty reasonably and is higher regarded for music reproduction, but is a slightly older model than some you might consider. Personally, having basic 5.1 DD and DTS meets my needs, but if you want all the new 6.1 formats, your choice of processors may be somewhat more limited. It's widely believed that having an analog-pass-through channel in the pre/pro will aid music reproduction, and many nice pre-pros don't have that capability.

You should really try and audition the new Classe CD/DVD-1. You can email Classe through their website to get the tech specs. http://www.classeaudio.com

Of the 3 processors you listed my personal choice would be Meridian. It's Home Theater performance is right up there with the Lexicon MC-1 and the Music is great as well. Even better the Meridian processors are the only ones at this time that have Pro-Logic II and they can be upgraded from Meridians website.

Your 3 choices are all excellent. If you're not too concerned about upgrading to future surround modes, the Classe' SSP-25 is probably the best for the money. IMHO, its Dolby Digital & DTS performance is just as good as the others and its 2-ch stereo mode is phenomenal (best I've heard from a <$6K surround pre). The only major drawback is the fact that it may not be upgradeable to the new multichannel formats (DVD-A & multichannel SACD). For under $2K, it's the best I've heard.
If you can audition these preamps (preferably in you own home), I would strongly recommend comparing them side by side. Good Luck.