Well... I never would have believed this, but no problems last night with new cable to ASI585MC, so I'm cautiously optimistic the problem is solved (I took up to 60 subs). For anyone else having problems with any camera, I'd be suspicious of the flat USB cables supplied by ZWO.
Note: I got my new cables from usbfirewire.com (they have shortys and you can also specify the angle of the plug(s)).