Well, I can't speak to the newer (and much better, I'm sure) Lexicon MC-12, but I have a DC-1, and IMO, it is NOT better than Dolby Digital or other discrete playback. It is KILLER for non-5.1 encoded material (use it for cable/satellite, and you'll even enjoy the commercials!), but I still watch all my 5.1 DVDs in THX 5.1, which adds THX post-processing. Of course, the Logic7 in the newer Lexicons is probably much better.
For 100% HT, I'd say you COULD probably go with the receiver and be happy. The only thing about a receiver is that you'll need to avoid difficult speaker loads -- stick with 8 ohm models and you should be ok.
Keep in mind, though, that you don't necessarily have to buy a new MC-12 if you want Lexicon -- DC-1s, DC-2s, and MC-1s regularly pop up here on A-gon, and I'd be willing to bet that one of those, coupled with good amps, would stomp the receivers you're looking at for the same price -- not to mentioned being much more readily upgradeable when Lucas decides he needs even more money . . . . ;-0)
For 100% HT, I'd say you COULD probably go with the receiver and be happy. The only thing about a receiver is that you'll need to avoid difficult speaker loads -- stick with 8 ohm models and you should be ok.
Keep in mind, though, that you don't necessarily have to buy a new MC-12 if you want Lexicon -- DC-1s, DC-2s, and MC-1s regularly pop up here on A-gon, and I'd be willing to bet that one of those, coupled with good amps, would stomp the receivers you're looking at for the same price -- not to mentioned being much more readily upgradeable when Lucas decides he needs even more money . . . . ;-0)