very happy with my DEQX HDP3
Having owned my HDP3 for 2 years I'm very happy with it.
I've also had great after sales support from Deqx and Alan in particular - for a sales guy Alan knows the technical intricacies of the box like the engineers who designed it.
The flexibility it offers is also its challenge - it's not trivial to get it setup to get the most out of your system, and I'm still learning how to drive all the features.
I originally set it up as just a 3 way triamp crossover. It took me some time to get to the point of setting up my 2 ways outside to do a semi-anechoic measurement, but having done the measurements once, you can play around with the speaker correction at leisure.
I'm not correcting the sub woofer responses as they crossover at 80Hz, so even measuring outside the windowing required would not provide any resolution.
One great feature I discovered when doing the speaker measurement was that the DEQX determined my tweeter amp was out of phase with the midrange amp, and asked if I wanted it automatically corrected.
I have done a small amount of room correction, but I typically move around the room a lot and find my treatment works better.
I have mucked around with the parametrics to dial in room curves etc which is easy.
There are subtle features that you don't find in the instructions, such as how to set the gain on the analog outputs to the power amps to get the right balance at the listening position - I've found it a great help to have other owners provide advice via forums.
You have the option of traditional IIR (Linkwitz-Riley or Butterworth) or Linear Phase crossovers up to 300dB/octave.
The speaker correction adjusts amplitude and phase response and time-aligns the speaker. Time alignment can also be done between a speaker and a sub to the listening position.
It won't allow you to set crossover slopes that are too steep based on a maximum delay threshold - given I only use it for audio (not movies), I'd prefer it to delay the other channels and let me run as steep a crossover as I want - I probably can, just haven't found that setting.
I run a music laptop via USB to an external USB/SPDIF converter to the XLR AES input on the DEQX, which allows me to keep my CD player as a backup and connect via SPDIF COAX.
The sound is fantastic.
If you're not a tinkerer, then if you go down the DEQX path I strongly recommend getting it professionaly installed. If you are a tinkerer, then still consider professional installation as a baseline and tinker from there (you would learn a massive amount about driving it while it was being installed also).
It's in a different league to the Behringer DCX 24/96 - I can't compare to the other room correction devices mentioned in this thread - I use it for the crossover and speaker correction - in that department I don't know of another product that comes close.
cheers
Mike