Since winamp will use windows media foundation now, it should take full advantage of all the encoders and decoders WMF has to offer. For example, we can still encode AAC.
https://en.wikipedia.org/wiki/Media_..._media_formats
If encoding/decoding support varies by windows release (I don't know if vista has AAC encoding, and I don't think windows XP and below has much of anything at all) then I suppose winamp would have to detect the system and remove encoder/decoder support accordingly...