In.
Out of curiosity, has anyone used the 'cascade' feature to gang two units together?
Yes, with my 680 and 680MKII. Works extremely well, except for the fact that there's an offset between the two (that varies each time you record) that needs to be adjusted for in post. But the control works perfectly and they stay in perfect sync.
Good to hear this is confirmed.
You might try turning off the pre-record buffer on both machines to see if the time offset then at least remains constant, and perhaps reduced, if not eliminated. Doing so helps with R44 cascading. Of course you loose the advantage of a few seconds of prerecord. Worth a try I think.