I had some of the same questions with my setup but it turns out that you can turn on EBA for the SL connection only (at least in the SEversion) and leave your G68 connected to input 1 without EBA enabled.

Are your 8k's already SL? If 8k.1 you would need to update to SL or to SE before you can take advantage of EBA. I believe if music is your biggest concern then an 818 followed by 8k to SE upgrade or the reverse would be your best bet.

The only problem with this setup is you would not have MRC with just the C10 or 818.

Gary

Main: 800 with LPS, 861v4, 818v3,8000.1SE, 96/24-6k C, 96/24-5k sides, DSP33 rears, M2500 + Velodyne 12", QNAP-MS600, Ruby, PS3, HD621, Oppo.
Games room: G68J, HD621, M33's front, analog ceilings rear, Velodyne 10"
LR- 6k 24/96, MS200, 800 with LPS