2 preamps is usually a bad idea unless you are looking to very very overdriven stuff. This is because one of the most desirable qualities of a pre amp is transparency, ie no self noise / coloration of the sound.

However, in this case you may be able to get away with it by keeping the signal strength coming out of the POD pre right down and feeding it into the input of your Marshal. Id start off with the Output, channel volume and drive knobs at zero. Then slowly turn up firs your channel volume than your output and finally your drive (you many not want to touch your drive knob) until you get enough signal.