Frodo 12.2 and MPC-HC external playback sound issues

I have XMBC Frodo 12.2 installed, and all of my MKV containers play fine with the default player. I do however want to use MPC-HC as my default player. MPC-HC alone works perfectly. However, when I configure XMBC to launch MPC-HC for mkv playback, the audio just repeates the XMBC "Select" sound over and over until I close out MPC-HC.

I am using the Aeon Nox skin, but otherwise custom Frodo install.