Obviously I'm biased, but I am going to give you my impression, since I've probably heard the PARC in more rooms than anyone else. We've used it full range with everything from very revealing Martin Logans to Genesis 200s to Kharmas to Von Schweikert VR-11s. At many trade shows we have 7 or 8 PARCs installed. Those rooms are a real problem, and the better the equipment, often the worse the problem. Keep in mind, the PARC is for bass only. I agree with the above posts, that you should correct the room as much as possible. Have the PARC do as little as possible. With the PARC, you will still need to deal with high frequency absorption, first order reflections, and diffusion. However, in the bass, correcting with passive treatment is frequently impossible to obtain. To absorb a 70 Hz bump, you are going to need 4 feet of fiberglass (that's depth--not surface area!!). And even if you were to put 4 feet of fiberglass in your room imagine what it would do with the rest of the spectrum. You would feel like you had a head cold just walking into the room it would be so over damped.
Bass has to be equalized, but that doesn't mean you have to use an equalizer. A room with good dimensions is the best way to deal with the bass, but many of us don't have that, and moving walls is out of the question. Absorbers aren't going to work for the above reason. Capacitive type traps, such as RPG Modex or Real Traps can help if the peak is modest and rather broad band (Q factors of 1.5 or less). Then there are custom designed and built Helmhotz resonators. These are large, heavy, and difficult to manage, but they work. Not all of us are willing to build and install one of these--in fact, most people aren't. So what's left? Active equalization.
We developed the PARC because we could not find a device out there that was transparent enough to run full range. Our company's primary business is designing and engineering rooms. If we can start from scratch, the room won't need a PARC. However, if we have an existing room with unfriendly bass response, the PARC is a viable tool. Without getting the bass right, we can not deliver a rewarding experience for our client--and often for existing rooms the PARC is the answer. We keep the signal in the analog domain which has not only great advantages in terms of transparency but also in terms of phase. In the bass the phase shift caused by the room is automatically corrected by the analog circuit in the PARC. This is not a fancy design that builds in time delays or anything of the like--in fact it's the simpliest--analog filters by their very nature have this phase shift, and it's the inverse of the rooms shift. Simple.
Okay, this is the most commercial post I've ever made, but since the question was asked I felt I should at least state why we developed the unit and what we've found. Now someone can dice me up for pitching the PARC.
