Make sure you've got a stereo mini plug that goes to stereo out on the other end of the cable either with rca or 1/4 inch plugs. If you are connecting directly to the Audiophile then you'll want the other end of your cable to have RCA. Make sure you've got a stereo cable rather than a "Y" cable which will put the same signal on both channels.
If the Audiophile had some sort of adjustable input impedance then that might be a help but it doesn't. I have never used Peak but you should be able to push the gain up on individual mixer channels.
I have found gain is something best made up in the analog world. I have never worked with a minidisc system so I couldn't tell you what works the best. You might ask at this forum:
http://www.taperssection.com/yabbse/index.phpI could see anything from a receiver to a compressor to a mic pre to a DI to a mixer having something that could give you the gain you're needing to the signal.