A bit off subject I know but you guys have helped me in the past and hopefully might be able to give me some ideas.

I run Primo on a double din unit. The inbuilt firmware media player is appaling so I have set the unit up to boot me into WinCE and run iphonetoday to give me a nice front end. primo works fine through this but I know the media player built into primo appears to be mono.

So I installed Nitrogen media player but this also plays in mono.I have also tried another media app and the same thing happens. Is this an issue with WinCE or should apps be able to output to all speakers

by the way when playing media using the inbuilt firmware it outputs to all speakers. Also Primo outputs ok as well.

The media player within Primo is mono, yes.
Both Nitrogen and NaviPlayer (either a good alternative to use as "External Program" within Primo) are stereo by default..unless something was 'done' to whatever version you have to make it mono only.
Don't know anything about your 'IphoneToday' front end, or what, if any, affect that may have on how things run. Also do not know if perhaps the version of WinCE on your device has somehow been modified or re-routed to not play stereo, but normally a stereo app run on WinCE will produce stereo sound given the appropriate stereo output/wiring.

I reckon this is down to the sound driver in the device, On my medion device if I run VolumeX there is a balance slider, this device will play music tracks using tcpmp in stereo, all my other devices don't have this balance control and play music in mono.