I use FM Acoustics P.I.T. interconnects, they are very good but very expensive. They are leftovers from my last system. But a good solid microphone cable from Canare, Mogami, or Belden, will work wonders with the Bryston. Hell, try Bryston's own interconnects.
As for speaker cable, regular old Belden 10 gauge from Blue Jeans Cable. This also works very well with the Bryston 4BSST amp and JBL speakers.
However, I would like to upgrade to the latest Bryston SC4 speaker cable. The reviews here say it's pretty damn good. Especially for the price! $9 US a foot!