As far as I know, the Strad has the aftertouch on by default (and I think it's always on). So maybe some element in your MIDI chain is filtering aftertouch. You can download MIDI Monitor here: http://www.snoize.com/ It's a MIDI monitor, but since I'm a PC guy I have never tried it, I was going to point you to MIDIOX, but it's PC only, and this one seems like its Mac equivalent. Then use it to monitor your Axiom's incoming MID, without starting Digital Performer and watch for Aftertouch data. If you can't see any, then maybe it's something with your Axiom, or the Motu Midi Xpress. If the monitor reads aftertouch data, then it should be on Digital Performer's side, but again, I've never used it. Cubase has a MIDI filter in preferences menu, so I'm sure DP has something similar.