Martykl don't get me wrong, the DEQX is a very good product. However the benefits of a unit like this has to be weighed against the losses that you get from the ADC (if used), the "not quite there" DAC's, and the digital processing. The controversy arises when people disagree on the weighting that should be given to the benefits and the losses.
The cons (as mentioned) are loss of resolution and an overly digitized sound. This is not so much of a problem when competing with low-end CD players or when the machine is inserted into a not-very-resolving signal chain. The signal still contains more resolution than most low to mid end speakers can handle - so the losses are masked, if you like.
However, the benefits of room correction, active crossovers with extremely steep slopes, group delay correction, phase control, etc. etc. are all there for the taking.
Do not underestimate the stunning results you can get from 300dB crossover slopes. I have heard the difference between the shallower slopes and the steep slopes, and the improvement in clarity is breathtaking. You can do things which are impossible with analog crossovers - for example, tweeters are typically crossed over at 3kHz with 12dB slopes to protect it from bass frequencies (meaning, -12dB at 1.5kHz, -24dB at 750Hz). With a 300dB slope, you could cross the tweeter over at 1.5kHz and still enjoy the same protection. There will also be no overlap with the midwoofer, since you can bring that up to 1.5kHz too.
IF you are like me and have a "finished" speaker with internal crossovers, you will not be able to exploit some of the best features of the DEQX so the balance changes markedly to the negative. Using the DEQX for room correction only is not worth the performance hit I get with the loss of resolution.
However, if you are a DIY enthusiast, or you can bypass the internal crossovers and are willing to purchase seperate amps for each driver, OR if the designer of your speaker did an incompetent job with the crossover or design, then the DEQX makes much more sense. In such a case the benefits will outweigh the cost.
Another thing. There have been a few threads on Audiogon recently about the evils of digital volume controls. This is because bits are thrown away prior to analog conversion - you lose resolution AND the signal goes closer to the noise floor. Room correction works by finding the null point in your room and subtracting other freq's to match the null point. So you can not get away from the digital volume control. If you are interested in room correction ONLY I would investigate an analog unit. I believe that Rives (who has posted above) makes one.
Disclaimer: no association with Rives, DEQX, TaCT, or any company.