I'm a fellow RM9 owner and also use an Audio Research LS15 pre. Very satisfying combo! Coincidentally, my RM9 also sits on the top of my rack, looks mighty pretty, don't she!?;) One of these days I'll get around to posting pics of the rig.
Re: the hum. I moved from a house in GA. to an apt. in FL. this past yr. In GA. my system was dead silent and yet in FL. I've got this minor hum. Event though it isn't audible at all when playing music it's like an itch I can't reach, yaknowwadI'msayin'!? Especially frustrating since I KNOW that the same exact rig was silent prior to the move. I've re-checked my connections, changed tubes, and tried switching IC's with no results. I simply had to accept the (apparent) fact that the fault lies with where I'm living and NOT my system. But man....that itch!!!!;)