I also have big sync problem, i experienced the weiredest thing on saturday, i was planning to play in sync with a TR626 and a TR606, using a dopfer sync box and a MFB502 modified.
Ok i will try to make it simple:
1st case: 2 drum machines are in sync, MFB and 606, if one starts the otherone ends up losing sync and just stops, this happens on both machines, depending on the times, sometimes the 606 stops sometimes the MFB.
2nd case: 1 drum machines, the 606, the midi latency is set to the - value of the overall audio latency of ableton. Everything runs fine, if i set he midi latency to 0, the 606 is runing but with a delay.
3rd case: the 606 and the 626, in sync, both machines starts, but sometimes the 606 loose the sync and stop by itself. The midi latency is set to the - value of the audio latency: the 606 is in sync, the 626 is running but with a delay. If i set the midi latency to 0, the 606 has a delay, but the 626 is perfectly in sync.
4th case: the 626 by itself, midi latency sets to 0. It runs fine.
so on the end i jsut used my 606
I use my UC33 to provide the midi synchro. this is with a macbook 2,16g and ableton 601.
It seems that the midi clock signal is too weak to take care of those machines.
The thing that i don't understand is that still with ableton5 i did some live using a 606, a 626 and a 505 in sync and I never had such a problem.
Do you have any idea of what can be causing that. Do yo plan to fix that.
Thanks
K
EDIT:
Forget to mention i'm off course on patern mode and not song mode