I'm having similar issues :/
I've discovered that dsp bypass on ( selectable per scene ) sucks the tone somewhat. I now use it only in true bypass. That helped a lot, but there is still volume drop when I engage any effect.
I use the 4cm in the loop of a JVM 410h. I haven't tried it in the front yet ( would kind of defeat the purpose for my use ), but from what I'm seeing / thinking it probably wouldn't help.
Maybe someone else will happen by with more insight, because I may be missing something too