Hey, I like you idea of using a thickening delay on one side of the stereo signal. I have been considering doing the same thing in my rig, but I know some pedals (especially time effect pedals to my knowledge) switch the phase nearly 180 degrees, which could result in noise cancelation. I was going to try using the DD-3 on one side of my stereo signal (after chorus), then a DD-6 after the DD-3 for longer delays (I don't want to use the DD-3 after the DD-6 because it would then put a short delay on my long delay). I do not know if the DD-3 would switch the phase, but that would be problematic – do you have any idea if it would do that?

Also, it is important to note that I think you must stick a plug in the direct out on the DD-3 to get effect only in order to use it as a thickener, otherwise it is a wet signal (both the direct and effect). 

Thanks,
Jon