libmpcdec 1.2.3 was recently released with a couple of major enhancements. (fast seeking and lower memory use)
Release Info: http://www.musepack.net/forum/viewtopic.php?t=347

I've modified BASS_MPC to use the new decoder, so AudioNUT (and any other program using BASS_MPC) can now benefit from the new library.

Tools Used:
- Visual C++ Express 2005 - avaliable from Microsoft
- Platform SDK - avaliable from Microsoft
- BASS 2.3 - avaliable from Un4Seen Developments

Alternatively, the plugin can be built with Visual C++ 6.0 (the preferred method, as this will generate a library with no dependancies)

To build the plugin, copy bass.h and bass.lib into the source code directory. Compile using the 'Release' target in Visual C++

Download:

Binary (ZIP): BASS_MPC (based on libmpcdec 1.2.3) Binary
Source Code (7Z): BASS_MPC (based on libmpcdec 1.2.3) Source Code

The original version is avaliable from Un4Seen Developments, source code from Maresweb


Very Important Note:
I offer no support for this, I have tested it on a ton of Musepack files so it should work. Use at your own risk!