http://cogosx.sourceforge.net/index.html a reasonably new mac audio player with mpc and ape support, claims to be gpl dont know if it actually sticks to it. if it is couldnt you use his decoders atleast for the mac version? it would be a start and on windows atleast ape/mpc capable players are not that hard to find (foobar2000 is my favorite but winamp will do it with the right plugins)
The license under which APE is release is not GPL compatible. That's the reason we cannot provide a decoder for it in VLC. Other GPL programs might be using it, but it's NOT correct, these programs might be violating their own licenses because of that.