I sold the MCintosh line for quite some time. I've only heard the proceed pieces in mention in other store demo's, and would have to say that, yes, they both make some good sounding pieces between the two companies. I'd say the Mac is a bit warmer and bodied over all, while the Proceed usually has a bit more top end energy usually, and is less warm in the midrange. The Proceed comes across more like Krell gear to me, and the Macintosh a bit more like a mix between Theta and Classe to me!! In ultimate terms, the Proceed's are probably a bit more extended and finished on top, giving a bit more air and top end detail (a smidgen). The Mac MC352 is not the last word in top end extension, but is 98% of the way there. Your key is going to be finding the balance with your system needs.
I'd have to say however that, as far as reliablity and quality control goes, I don't think the Macintosh stuff is as tight as perhaps it once was!!...?
At the very least, during the period of one year, we had severl Mac pieces go back defective out of the box!!! Preamp's, amp's, pre/pro's, and CD/dvd players!!! We never even had as many problems with the Parasound or Adcom stuff we sold more of!!!...seriously!
I must say though, the Mac stuff is nice when it's working (ha). It mates well with a lot of higher end speakers (that tend to be a little on the analytical side sometimes). I like the Mc352 amp enough, and it sounded really good on things like NHT 3.3's, and Maggies. I think the Proceed stuff alway's tended to sound a bit dry and zippy if not properly matched with gear. Not to play it down, it's just not recessed in the slightest, and it's balance tends to be unfriendly with some of the more neutral, dry, or analytical set-ups.
If you need warmth and body, I'd say a functioning Mac would do (they should take care of any problem should it arrise. Infact scream and yell if they don't!) fine. If it's a wamish bodied speaker (Vandies, B&W's, Alon, Celestion, Sonus, M. Logan, etc) who isn't so easliy tipped into brightness (i.e., Thiel's, Maggies...Revel's are marginal), I think you'll do well with the Proceed...if these are you're choices.
Haven't heard your speakers though, so maybe you could describe the character and catagorize em yourself!
Have fun...