I have to agree that upgrading your 8k's would provide your with the largest improvement in sound quality if you are looking to change your system over time.

You can hook your C10 directly to them using SpeakerLink and also enjoy the advantages of EBA in 2 channel. Your G68 is no slouch for movies and you can save your money for the 861v9 when it comes out.

I think the MS600 would also be an relatively inexpensive sonic improvement to the C10. Others may disagree.

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