How about NONE...Ive owned a MC352 for 10 years and its always been plugged right into the wall socket directly with never a problem (and I move a lot), the problems start when I’ve used cheap devices in the past (they color the sound badly and rob the dynamics and emotion). The MC452 has a fully regulated power supply...anything but a very high dollar (Dave is right) unit will just get in the way of really great sound But, if you must here is a link to a great affordable product that I have heard is one of the least offensive sounding...And Please Please pull that Monster Cable Conditioner off your system...It should be nowhere near a MC452.
http://www.audience-av.com/conditioners/index.html
Matt M
http://www.audience-av.com/conditioners/index.html
Matt M