Just to note Stan, that as part of the transition to HTML 5, I have been making three sound files available for each listening task. The mp3 (which is usually my original file), the m4a and the ogg. My HTML code offers them in that order. The reason why is that mp3 usually has the best sound quality as the other two are often converted from that file. It has also made my code work across browsers and versions of browsers quite well as the mp3 is still needed for some like slightly older versions of IE.
As for audio conversion, I have found that exporting out of Audacity (or other commercially available sound editors), has been the best for me in terms of sound quality rather than the convertors that I have found on the Net.
Tx and once again, I have found your Hot Potatoes Hacks book very useful.