Hello Mathieu
To know if an audio interface is compatible with WO 5 , check if WIN7 WDM driver is available.
We use the Echo Fire12 or 8 with WO 5 & WiN7 X64 on different sites to play 8 channels and it workd fine.
http://www.echoaudio.com//Products/FireWire/AudioFire12/index.php
Eric Lambert
VIDEMUS PARIS
www.videmus.fr