Thanks for the replies. So I guess the dedicated sub EQ might go a little further than Audyssey. I wonder if anyone has ever compared the sub settings done by the dedicated sub EQ setup with an Audyssey EQ setup on the sub?
You have to be much more specific, I think, about
which dedicated sub EQ. Ok, by reading the OP, I think you are implying EQ that's already built in to a commercial subwoofer. Of all that I have seen, none will have better resolution than XT. However, what's nice about the built in stuff is that it is adjustable to taste, whereas with XT it is not. What you can then do is calibrate with XT, and then fiddle with sub adjustments to taste.
OTOH, if you are not limiting the discussion to built in EQ on a sub, but outboard devices you can add, then opinions will start varying much more. Whether it's a DCX2496, or AntiMode, or the XT built in to the SVS ASEQ1 which is designed to work with XT receivers I believe.