I've dipped in and out of compressors fro the last few years, and I bought an Aphex Punch Factory (the older 1404 optical compressor) on here, and my OC2 and DOD FX25 are MUCH happier with the steady input that they receive after the compressor - particularly the envelope filter.
I've got a DHA VT1 EQ on the board too, with I use for a little bit of grit (not sure that it's a noticeable amount of compression), but putting my compressor at the start of the signal chain has made a massive difference. I don't think I've turned it off since I put it on the board.