I've been running a 990 connected to a B&K 200.7 amp for the past two years. Recently I connected a blu-ray player (Samsung BD-P2550) via the 7.1 inputs, but a Pioneer Elite was previously connected that way. I have never had a ground hum, but now I get a hum through the 7.1 input, but no hum through optical couplings>

Any recommendations?

Are they plugged into the same receptacle?

Make sure all of your equipment is sharing the same common ground. If your previous BRP had a 3 prong and the new one has a 2 prong plug, it is likely that the ground is slightly different. You may need to try to ground the new player to the 990. Optical is essentially immune to ground loops but everything around it isn't. Check to make sure your interconnect cables are not running next to a power cable. You may also have to check the circuit you are connected to for other sources of noise which is feeding back through your ground. Good luck, keep us posted.