Re: How to connect a distortion pedal in order to use it as a preamp?
Most pedals are designed for instrument-level signals, but most effects loops are designed for line level. It won't hurt your amp to run it without anything plugged into the input, but with many distortion pedals you might need a booster to get a signal strong enough to drive your power amp. For this type of arrangement guitar > pedal > FX return would be the way to go. Feeding a distortion box that's looking for a weak guitar signal with a line level from your effect send could produce weird results.
Then again, I've heard of amps where the effects loop can be set to run at instrument level- they provide that option specifically so players can run pedals in the loop. So check your amp for it- if yours has that capability you're golden. If not, there are certain pedals which are designed to act as preamps, some of these might have enough power to push a power amp- I suspect many preamp pedals probably have an output level switch for line or instrument level. But your average distortion pedal (unless it has huge output) would likely not have enough juice to do well in that situation.
But it can't hurt to try a pedal or two and see how they do.