Your MD8 has 8 direct out feeds that can be used to send to an audio interface on a computer. You'll want something with 8 inputs, like a Tascam 16x08, Focusrite 18i20, or Presonus 1824C. Then it would be a simple matter of feeding the outputs into the interface, loading up a proper multitrack capable software, like Reaper, and hitting record on the computer and play on the MD8. It should be a very straightforward conversion.
Once done, you'll have 8 individual wave files on your computer for later mixdown, modification, etc.
See Page 85 of the user manual for a very basic explanation of the setup.
The direct outputs are -10dB, so you'll want to use that setting on the interface if given a choice. You'll need 8 cables with RCA to whatever connector your interface uses. Most likely it will be an 1/4" jack, either TS or TRS.