I constantly had hum in my speakers no matter what I did with my CM2. A shame because I loved the Rogue sound but it kept me from moving up the Rogue Audio chain.Same experience here. I also had hum with the Stereo 100 amp. Ground hum seems to be the fly in the Rogue ointment. Apparently they finally deemed it necessary to address this problem in the CMIII.
OP, consider Audio by Van Alstine products. I have their Fet Valve CFR preamp. It's very quiet and takes on the sound of whatever tubes you choose to run. All the parts are of high quality.
And yes, separates will be an upgrade over your CM, but the components must have good synergy. The PS Audios are an easy choice if you have the dough.