Using two AtoD channels - they're interacting?!

[tenaja]

I'm finding that in my setup, it needs at least 30ms between successive AtoD channels 'samples' - hey ho.

This is the case with every PIC, and for each and every a/d reading. It is called the "charge time" for the sampling capacitor, and is most often the bottleneck for sampling rates. (Some PICs charge it faster.) With a single channel it is often not noticed because the sampling cap is charged while doing other things, or because you get an "old" reading from the same channel.