Playing in pubs there will always be constraints. In my experience, an un-miked drumkit is plenty loud enough and levels get set accordingly. A bit of kick drum through the PA can help. Good sound separation only happens when band members listen to each other and are sympathetic. As stated before, if you don't have a sound man out front I can't see the point in all going through the PA and it seems like a bit of a modern fad. We normally get a couple of our trusted punters to give us a bit of input as to what the sound is like out front.