I've got a bday coming up, and instead of a chair, I'm going with a compressor and a few other gadgets. So my question is, what's really the difference in the dbx 160 line?? I've seen the X, XT and A versions, but not entirely clear on why they're so different, if they even are. I know the A seems to be at the top, but don't know where the others rank. I'm also checking out an Alesis 3630 per some good reviews, along with Aphex's Expressor.. But from what I've seen on here, nothing beats a good old dbx 160-line compressor... thoughts?