The Roku uses the ID tag on each music file for organizing purposes - Title, Artist, Album, Composer, etc.
Actually, strictly speaking, that's not quite right. It is the server which is used (Itunes, Firefly, whatever) which accesses the tags in the files. The SoundBridge allows searches based on the information provided by the server (it does not know where the strings come from) and when a file is being played the title and artist etc. again comes from the server and is not extracted by the SoundBridge from the tags in the file.
The choices offered when browsing are also often a function of the server, although the SoundBridge has its own search criteria as well which are supported by FireFly and this does include a Browse Composer option separately from Browse Artist.
Tags in WAV files are possible but are not that widely supported. If the quality of the WAV files is desirable, then it would be better to use a lossless format such as FLAC or Apple Lossless instead. Note that the SoundBridge does not support FLAC natively, and so this can only be used if the server application which is being used can transcode the FLAC to WAV for streaming. Firefly supports transcoding under WIndows and Linux, for example. Apple Lossless is supported natively by the SoundBridge with the 3.0.xx series firmwares.