Apple Airport Express won't play WAV files

My music is all on my iMac HDD. It is connected over wireless network to an Airport Express, which is plugged into a Marantz SR7007 using an ethernet cable. When I attempt to play a WAV file, I get a message that says "File Format Error". How do I play WAV files on this system ?? Thanks
Thanks for all your suggestions. I have direction to go in now. I'll be out for a few days, but I will report back when I have something to report.
Back again. I figured you how to convert WAV and APE files to FLAC using XLD. Now I can play those files thru the AE, but only up to 16/44.1 kHz. If I try to play 24/88.2, or 24/96 FLAC files, I get lots of dropouts. Is this a limitation of the AE, or of my router ?
This thread on Apple forums sounds similar to your problem:
Airport Express - Digital audio output - and Jitter