Re: Pedal question
Most "OD" pedals work well, in one way or another, in front of a distorted tube amp.
One of the classic ways to use a tubescreamer type of pedal is to use the gain really low and just boost the volume on the pedal until the amp gives up the goods.
Some low-wattage amps may turn to mush if you hit them too hard like that but as long as the amp is up to task, you can almost always use an OD pedal that way for some really nice results. The MXR should be able to do this well.
If you're actually gonna use the "gain" in an OD, you'd be wise to play whatever OD first to make sure you like how rough or smooth, how bassy or trebly, and how clear it is. Using too much OD pedal gain can muddy things up if the amp's already cookin.
This ALL depends on the amp in the end, because you're gonna be juicing the amp to bring out more of it's own character, just with a little flavour twist. It won't turn an ac15 into an ac30, it won't turn my JCM 2000 into an 800.