Alot of what is coming through the PA already will have a fair amount of compression, you definitely dont want to compress it alot more on top of that. It will start to get that FM sound. I would think (although I dont know) that Doug is talking about using a compressor to keep any overs from occuring. Basically the threshold of the compressor should be set so that it only starts compressing during the loudest parts of the show. That way you can optimize the volume of the board feed and not have to worry so much about levels. This would also preserve the dynamics that are still present in the feed. A limiter would also work fine, but if the levels got loud enough, and the limiter really started getting hit, it would be alot more noticable than a compressor (and n ot nearly so "musical"). Have you ever thought about getting a decent rack mount pre with insert points? Than you could insert whatever you might need (compressor, limiter, etc). This would also allow you to use higher quality compressor, like a Drawmer or the like.