Standalone room correction with adjustable delays, plus manual adjust? You didn't mention the overall integrity of your system needs. So, in that case, I'd likely steer you in the direction of the Audyssey piece. Especially on lower priced end -I think it's like $2500 new, and likely $1000 used, or cheaper - this makes sense. It tixes your time domain, has adjustability, a good sonic rep and, at every least, addresses most midfi/hi-fi entry systems, offering to fix your major concerns for better sound performance.
For cost no object perfromance, my experience suggest that if you're putting together a high end 2 channel system, and typical domestic small living space is what you're dealing with, than you insert the Rives PARC, calibrate out your ALWAYS troublesome bass mode issues, and forget about it! You are simply NOT going to get more full frequency sonic purity through your system than that, fundamentally. The rest is - as always - mid/high room treatments, corner traps, and whatever else you can do to fix the "un-EQ'able" excess Bass energy, which exists in most small home spaces (exceptions: very large typical rooms, or rooms open to much larger areas/spaces).
We are of course talking "stand-alone" processors here. I like what Ive experienced from hearing the stand-alone Audyssey processor, for dedicated home theater SEPARATES based systems ok. But, if money is no object, I still think that going Rives PARC -multi channel version setup - there too, as you simply will not beat the sonic transparency! And, basically, you're really only trying to EQ the bass issues - unless you simply cannot move your speakers to locations where they'll sound their best. So, in the case of speakers up in corners, or inside cabinet enclosures, etc, yes, I think the Audyssey works the absolute best as stand-alone here. Youll trade total transparancy and refinement for fixing other major fundamental issues in that case. So, I'm really only using it for HT duties, where ultimate sonic transparency isn't number one concern. The Adyssey works in analog domain, I believe.
If one can place speakers for maximum overall mid/high frequency performance (as well as best allowable bass response characteristics, fundamentally), I'm reaching for the PARC, myself! And that' 2 channel or multi, btw. If it's a dedicated typical mid-fi HT system, then Id chose the Audyssey.
I try to avoid the Audyssey scenario, however, by simply using a better AV pre/pro that already has built in Digital domain processing anyway! Then, the outboard becomes an irrelevant issue, of course.
Anyone else here disagree with the PARC as being beatable for performance, for your EQ issues? I mean, if you need miracles done to your sonics, got speakers placed in some cubby-hole, and you know nothing about placing a loudspeaker for best sound anyway, then why would you care to look into fancy outboard EQ's anyway? That's what I'd ask myself.
Yes, PARC for high end, and Audyssey for typical hi-performance mid/entry hi-fi multi channel (Mostly HT ) systems.
Not sure what else would trump here...really.