@OP - Are you playing music through the iGo application interface or through the 2DIN radio interface? I think that's an important difference to be aware of. I would only use iGO to play the music if you have to - otherwise, use that function of your 2DIN (to help unload processing from iGo).
Also, I agree with @Boki_srb - a lot of WinCE head-units don't use internal memory at all for "applications" - just OS. For example, on my Rosen 2DIN WinCE headunit, everything iGo related is stored on the SD card and there is no internal storage to put it on even if I wanted to (plus the 2DIN is hardcoded to run the app from SD - and there is no way to change the location of the app it runs). I think that most WinCE 2DIN units are designed like this. Plus, it make it a LOT easier to update/change things when everything is stored on SD card (sys.txt entries, add skins, add UX files, etc) - and also, like mentioned, you can usually get SD cards that are faster than the internal storage anyway.
I would avoid trying to "separate" the iGo app and it's "content" on WinCE devices. I can understand it for Android, but WinCE is very different in "design".
Sent from my HP SlateBook 10 x2 PC using Tapatalk