[LAU] S/PDIF Passthrough and stereo files

Hello, I am currently setting up a HTPC, for my use and also for the family. My sound card is M Audio 24/96 Delta DIO, connected via the S/PDIF optical link to a A/V receiver. Software mostly used is gxine and rhythmbox. For mixer, I use Envy24control. For DVDs, gxine audio config is set to passthrough and Dolby/DTS works fine, with Envy24Control Patchbay/Router settings to S/PDIF out. For stereo music mp3s, ogg and flac formats are read with Envy24 settings to DigitalMix. What I would like to avoid is having to switch between S/PDIF and DigitalMix in Envy24 depending on the encoding of the file (Dolby/DTS on the one hand or mp3/ogg/flac on the other), as I aim to make the system as easy to use as possible. One solution would be to avoid passthrough in gxine settings for Dolby/DTS but that would be detrimental to sound quality for DVDs, so it is not an option. I have tried playing stereo files with gxine, but even though I can keep the Pasthrough setting, I still need to set Envy24 to DigitalMix. I do not really understand why a stereo file cannot be passed through directly to the S/PDIF under the same conditions as a Dolby/DTS one. My purpose is to send the data as is to the A/V receiver, which seems to be perfectly able to handle whatever it is getting. Any explanation, hints and solutions will be very much appreciated. Albert