@yyzsantabarbara - Firstly I must remind you that my & any other replies here are likely to be rather biased towards DEQX - you might get more balanced responses elsewhere!
Having said that, the single feature that probably gives it an edge are the speaker measurement & correction algorithms which I don’t believe are available in any of the others mentioned above.
Lyngdorf 3400 TDAI
I’m not familiar with this - it handles room correction & crossovers & is Roon ready. This product does not appear to have speaker time-phase correction though.
Linn SELEKT
I’m very familiar with Linn Exakt which (as with Selekt) uses room dimension/material based ’space optimisation’ calculations. It can produce very good results although DEQX does have greater transparency, sharper imaging and a more realistic sense of the soundstage. Bass is also tighter and more defined via DEQX, no matter how much effort I put into improving this on the system I set up. Logic suggests to me that this results from actual measurement of the speakers being used (via DEQX) vs calculations (via Linn).
Linn Space Optimisation can get close to DEQX but the two systems I am comparing are ~$350k Linn vs ~$85k DEQX (which makes the latter somewhat of a bargain!) Calculations do not match the accuracy of a mic based processor & when we measured the Linn room separately using REW, some of the auto corrections were inaccurate by comparison - manual adjustment after using a mic improved things.
However one aspect that I prefer with Linn is the ability to set individual eq for each channel, as opposed to DEQXs combined eq approach.
Anthem ARC2
I have listened to a system using this processor & as with Lygdorf, it handles room correction & crossovers. Although ARC doesn’t work in the time domain (speaker time-phase correction), it does manage room correction better than Linn, especially if aesthetic considerations preclude acoustic treatment.
All of the above will be very good for room correction if that’s your main priority but if you are looking for measurement based speaker correction AND room eq then only the HDP-5 covers all bases (preamp, DAC, speaker correction, crossovers, sub integration, room eq, Roon). The clincher for me was the fact that the mic FIRST takes a clean measurement of the speaker, corrects each frequency for timing & phase across all drivers and THEN room eq is applied separately afterwards. As I said previously, this makes by far the most significant impact to the quality of music produced.
As far as room correction itself is concerned, my own opinion is that acoustic treatment is the most effective solution, backed up with eq to address only remaining bass peaks.
(...yyzsantabarbara your forum name implies where you live - we have family there & spend many months a year in town so if you do decide on any of the above I would be interested to listen)
