Well Chrissi and I went down to Glenn's studio this week and we've realised we have the SAME problem BOTH on the mac and pc. Ableton 3.0 doesn't sync to SX2 via rewire properly. You get this annoying buzz when you rewind to bar 1 and if you set your loops on something later like between 9 and 11 you get a glitch at the begginning.
This IS workable but I'd love to know if anyone else has had this problem and whether they've been able to fix it.