I asked Oliver the same thing a while back, and the only useful outputs available are the mixed pre and post GB amp outputs.

I am looking into ways to reduce noise on dmgs too, thinking about swapping out the electrolytic caps for new ones, and trying to reduce the cpu noise and power supply noise using more bypass caps. I prosound all of mine, and whilst it certainly helps it does not get rid of the whines and clock noise, I believe that these can be reduced though, backlight and flash carts do make the noise worse.

I'll be interested to hear how it sounds with the 470uf and prosound.