Yeah, well you revived a 7 year old thread...
It was the solution 7 years ago.
Make a copy of out_ds.dll as out_ds2.dll,
Configure out_ds2 the same as out_ds, except for the Output Device
(which naturally needs to point to the respective soundcard),
Then load both of those into Multiple Output.
If they're still a bit out of sync, then sorry, but it's not my fault
Different soundcards/chips tend to behave like that.
It would probably be more in sync if you were using two identical pci(e) soundcards.