I had some pedal time with my Marshall DSL40C this morning. Actually it started last night but the good part of it happened today. I connected some pedals through the FX loop feature of the amp at the rear panel, the cables were long enough to rest it on the amp's top.
What's the difference if one does it this way? This connection allows the pedal to be connected after the pre-amp section so it sounds different compared to regular guitar-pedal-amp connection. The DSL40C blends well with the pedals in this mode, it needs more volume to ensure that the pedal's output does not overpower the amp's pre-amp section. If you refer to specialized amp heads, many of the FX-loop feature has an independent volume knob, this way, we can control how much influence your pedals have in the chain. This feature is absent here.
With any Tubescreamer/ Tubescreamer clones/ drive type pedals, the DSL40C sounds very creamy. In fact, it's able to take away some of that signature Marshall sting if you don't fancy that in excess. I know this amp likes distortion type pedals (no the intense metal type) instead, to make it sound very fierce but watch your pedal's tone control, do not let the top end get out of hand, otherwise you'll hear too much high frequency in there. With any distortion units through the loop, I need not raise the amp's gain too much, in fact, it's more fruitful having it at the half-way mark.