The Yamaha MD-8, and other multitrack Minidisc units,...
use a specialized "DATA-Minidisc", which is a bit more expensive than the "normal" stereo Minidiscs. The "normal" stereo minidiscs may be used, but they'll only record in stereo. For 4- or 8-tracks on Minidisc, you'll need "Data-Minidiscs", specifically.
The MD-8 has an Aux-send/recieve for external effects "loops", and also "Insert" patch points for effects, specifically on Inputs #1 & 2 too.
The MD-8 has punch-in/punch-out capability, that can either be worked with the common foot pedal, or set up to "Auto-punch" by programming it into the "console". It works like the typical punch-in/out you'd get on tape recorders, only more seamlessly. The MD-8 has a "no-gap" punch, like you'd expect of any digital recorder.
Minidiscs can be erased and rerecorded a million times, without degradation.
/DA