Well, first of all, you have very nice speakers.
I recently sold a few speakers (including Revel Salon2, B&W 802D2, KEF 201/2, & Philharmonic 3) and I'm in the process of getting 5 RBH SX-T2/R speakers. Hopefully will have them soon.
I've also heard about this issue with the Arcam and other AVR. Some firmware updates might fix similar issues, but unfortunately there are no guarantees.
If you can return the Arcam, that may be the best solution. Otherwise, perhaps someone here may have an answer. Good luck!