I own a Boss DD-6 delay and I'm having some issues with it.

When I use it with a clean/lightly overdriven sound, the delay acts like I want it to - the initial repeat is about 3/4 softer in volume, and it decays nicely. When I crank the distortion up, though, the delay gets really harsh - the repeats are pretty much at the same volume as the initial note, and it doesn't decay well.

I used to think this was an issue with my amp, since I had a SS amp for a while - I just upgraded to a Crate V16, though, and I'm having the same problem. My chorus pedal seems to suffer from the same thing.

Do I need to get an external FX loop to make it sound right?
From what I've heard, time based effects like delay and reverb should be applied after distortion, so unless you use a pedal, I think you should probably have an FX loop. I don't have any first-hand experience with pedals, though.