I have the same problem with my Heartbreaker. It seems that the master volume controls for each channel also serve as the return level controls for the effects loop. I hate this design. If I have the "Lust" channel set for clean or overdriven rhythm playing, and the "Love" channel set to boost, the master on the boost is set lower because of the volume boost and the effects lose any punch!
I see what you are saying, that really helped. Thanks. I am running a Boss rc-2 dc-2, ph-2, dd-7, and a mxr Carbon copy in the loop. No return level....