In file /etc/opkg/distfeeds.conf remove all # from all lines.

Run

opkg update opkg install mpc

I'm working on same project and have another problem. I can not play radio stream. MPC says ERROR: Failed to decode http://icecast6.play.cz/radio1-128.mp3.m3u. I can play single mp3 file from URL but not mp3.m3u file. Can you do that?