I also have a MKIII with the 400BH power amp section. Over the years it's been my experience that on the older PVs the comp was much more of a limiter to save speakers when the amp is pushed really hard versus a more musical soft-knee compressor. It seems to be after the EQs and post-gains, but before the crossover and power amp--but I haven't looked at the schematic in a few years--could be mistaken. Really a "try it and see" kind of thing, depending on your usual stage volume. I love my MKIII but wouldn't hesitate to trade up to a newer version. On the other hand, I have zero interest in the older models even though they are bulletproof and didn't suffer when compared to the other amps made around the same time.