I'm actually not sure why you'd need a preamp, a battery box (eg SPSPSB1) will power the mics and provides a loud enough signal for the recorder.
I'm sure someone more technical than I am will chime in here.
By the way there are two versions of the CMC8s - the older one used larger AT853 caps, the current one has ES943s. Both can overload (brickwall) at high volumes, and the answer is to phantom power, or use / build a 3-wire battery box..when is someone going to put this into production
Are you happy with the iRiver or does it drop samples? If its reliable, stick with it.