I am finding my music library via Firefly, but Soundbridge says "unable to play" the music files I choose.

Is this likely to be wrong file type? If it is where can I find the definitive list of playable file types please?

Whether the file(s) you unsuccessfully try to play is/are of an unsupported type or not I can't tell; you forgot to mention which one it is!

However, a quick browse through the soundbridge product pages on the roku hp would have provided the answer to your second question. In case you didn't find it, go to the FAQ

http://soundbridge.roku.com/soundbridge/faq.php

and scroll to the "Music formats supported" section.

Many thanks. That information is really useful.

Nor sure about the "quick browse". I find the pages muddles and disorganised.