I'm relatively new to this so bear with my poor vocab...
I'm running a Yamaha HTR-5640 (6 or 8 Ohms) Receiver (open box special at Best Buy - $219), Magnavox DVD Player, Comcast Digistal Cable and 5.1 Yamaha NS-P320 surround speakers (6 Ohms). I've set the receiver to 6 Ohms

My receiver keeps shutting off when I get to about -38.00 dbls - which is plenty loud, but I don't think the capacity of my 60 watt fronts/40 watt rears. When I turn it back on I get a message flashing "Check Speaker Wires". The wires are new 14 gague, I've checked them and I'm using banna clips, so the speakers wires are fine.

I had this problem when I first set it up and was running two big Yamaha 8630 speaker towers (8 Ohms) up front and the 60 watt (fronts) as rears and center (6 Ohms). My receiver was set to 8 Ohms at the time, and the same message would flash when I went above -50.00 dbls. When I replaced the fronts with the NS-P320 5.1 surround set of speaker and set the receiver to 6 Ohms I thought I had the problem figured out. Lo and behold it's shutting off again, just at a higher decible. Why?

Additionally, I'd love to have it set-up where I can run my A channel with the surround system (6 ohms) and the B channel in another room with my towers (8 Ohms). Will this ever be possible?
Any help is much appreciated.