Your test will exclude the Yamaha internal DAC, which for now, seems to be the heart of the issue. If you have a full refund warranty on the Cambridge, I think it would be best to break it in for as long as you can, then compare it to the Yamaha/DVD combo at home. If there's still little difference, it would seem to me to be a $400 (plus cost of i/c's) no-brainer.
Trust only YOUR ears (or those of a trusted friend). If you can't hear a difference, chances are there IS no significant difference.
Trust only YOUR ears (or those of a trusted friend). If you can't hear a difference, chances are there IS no significant difference.