What Herman said.
I’d say you probably don’t need to reflash your nslu2. You should be able to uninstall your existing binary with:
ipkg remove mt-daapd
As Herman said, you’ll need to then get the mt-daapd nightly ipk onto your slug somehow, as well as the libao ipk. Install them both (libao first):
ipkg install libao_whatever.ipk; ipkg install mt-daapd_cvs-whatever
The problem you are going to find is that there isn’t (afaik) a program to transcode wma-lossless on the slug.
the version of ffmeg that’s in unslung won’t do it. (I just tried).
Lemme scratch around a bit and see what will do wma lossless, and see how hard it looks to port.