Atik Titan maybe? Haven't used one, but it has a modern CCD, can run at moderately high framerates for planetary and is cooled, so will work OK for DSO targets. Pixels are a bit big, but it should be reasonably well matched to both of your scopes if you get a Barlow for the C8/planetary. Probably a good way to dip your toes into this very deep pond.
http://www.atik-cameras.com/products/info/atik-titan
Would recommend a mono camera. You will be able to produce black and white pictures straight off and, if you get the bug, can get a filter wheel and filters for colour later on. The main reason for suggesting mono is that, when you get the next camera, the mono Atik should be a good guide camera.