The idea I have to come up with a normalization offset is to look at the requantized frequency values coming out of the Huffman decoder to determine the absolute peak.

Normalization is great, but I don't think the scaling factor should be based on the peak level, as this is a very "local" criterion. RMS (the average energy in the signal, measured over the whole song) sounds much more useful to me. And it shouldn't be much harder to implement than just peak detection.

And if you provide the back-end, I would be willing to do a simple Windows front-end, also GPLed.

Daniel