I actually thought about that last night and came on this morning to ask about something along those lines! Here's what google found (although this is comparing the floor models rather than rack mounted...): XT is $399 retail, X3 is $499 retail XT has 36 guitar amps, X3 has 76 XT has 84 stompbox and studio effects, X3 has 98 XT has no vocal preamps (or vocal input), X3 has 6 XT is USB 1.1, X3 is USB 2.0 (faster) conneciton XT can do one tone at once, X3 can blend 2 patches together XT has a smaller LCD display, X3?s is nearly double the size XT has traditional out, X3 has S/PDIF and XLR out in addition to 1/4? jacks The HD is actually a lot cheaper than I thought, but I'm a rack mounting fanboy... Not a fan of the rat's nest of cables that pedals tend to bring about, much prefer everything in a nice neat box. Plus if I'm using the thing as a preamp then I'd need to take a power amp too, so having it rackmounted just makes sense. xx