I have an iPad 3 which I would like to use to play music to Bluetooth speakers in the background while I play various games and the like. The problem is that the foreground apps interrupt the sound of the background radio app. In Windows you can control which programs are allowed to output sound with the volume mixer; similarly, is there any way to lock sound output on an iPad to one background app?
Sorry but that isn't possible on an iPad. Each application/game has the option/ability to allow the background music to continue or to stop it and use its own audio.
You would have to ask the developer of each application to add an option to allow the background music to continue instead of interrupting. Good luck with that. ;)