If the wiring will be in conduit, you should have no problem picking up something simple - I'd probably go with 12ga. Something like Keta's Canare would be a good match. If you were running through attic or crawlspace areas or dropping loose in the wall, the cable should be plenum rated, which would eliminate most or all of the stuff at places like Home Depot and the Canare (according to Canare's site, none of their audio cables are plenum rated).

To passively bi-amp (no external crossover circuit), all you need is a splitter at the pre-amp output on the 950.