Hi, I wound up buying a Behringer Monitor1 passive monitor and volume controller.
See this link.
xlr in from the pre-amp, xlr out to the active speakers
Since it was the active speakers that were louder, i use it to reduce their volume. The passive Klipsch driven by the mc 275s are at 100% of whatever volume i've chosen on the preamp. The atc passive speakers are usually run at 75-80% of full volume