Well, if your plan entails sending the material to a mastering facility to have them do their magic, I recommend not compressing at all. Unless you have the top of the line dbx compressor (did you pay about $2k for it? If not, is is their budget stuff...) you don't have a compressor that can work as invisibly as the stuff frequently found in mastering studios. I am looking at mastering quality limiters right now that cost in the ball park of $4000! With my past experience of using stuff that expensive, you can bet it is a whole other world of compression then what you are using.
If you just have to use your box though, I would keep it set to about -6 on the threshold, 1.5:1 ratio, attack fast, release about 100ms. Anything more then this will start to really do some damage with a cheaper compressor. Those settings themselves could do some damage, but, they should work okay....
Ed