Whats the difference between MultEQ XT and MultEQ XT32?
There's two main differences, the first is precision. Audyssey MultEQ XT is no slouch; it's way more precise than just about any competitive system, using sophisticated FIR filters with hundreds of control points per channel. And yet incredibly XT32 goes way, way further with substantially more precision than XT — four times more precise for the subwoofer channel alone, where calibration is most beneficial.
The other difference is that some implementations of XT32 include the equivalent functionality of SubEQ HT, which basically means discrete dual subwoofer calibration.
Having said all that, MultEQ XT is so good that the law of diminishing returns applies — while XT32 is indeed significantly better, unless you have dual subwoofers or a room that really struggles with bass, you might not hear much difference.