It's taken me a while to get back to this, but I basically had a support call open with Quest (who own the DR series now) for a couple of months while they troubleshot a problem we had with the driver. Basically the driver would fall over randomly. Sometimes a few days would pass without issue, but it would always crash eventually, usually under heavy load.
To give them credit, Quest eventually rewrote the rdcifs driver file which seems to have done the trick. It's been running on 5 proxies without issue for about 6 weeks now. They tell me that the changes they made will be incorporated into the next driver release.
So, I'm now a happy customer, and have bought another 2x 36TB of expansion