It would be cool to route different effects through different audio devices for different sounds, eg the spotter could be routed via computer headphones, while all other SFX go via HDMI or CoAx or SPDIF; this would allow user to wear headphones (under helmet, for extra realism ) with clear spotter audio, while road and engine noises are routed via external speakers. This may also open up the multi (5.1/7.1) debate issues.
This might be a good idea, but you have to think about the family at night ... not everyone can play with the speakers all the time
seems like a strange request. I do appreciate what you're getting at - but personally I don't think that's necessary. You could consider enabling both your headphones and speakers at the same time and see if that sufficed, but you'll obviously get an overlap of sound through both, rather than selectively having just the spotter through the headphones and everything else via your speakers. Quick video re: Win7 on enabling both speakers and headphones and this should work on newer versions too, but I haven't done it myself personally.
...I was also thinking about this again after my first reply yesterday and I'm wondering out aloud if it would be possible to modify the positional audio settings for the spotter in the game? I don't know the answer to that, as I haven't looked into it - but if you could - then the most realistic solution to what you're getting at, would be to modify the positional audio for the spotter, so that the sounds are positioned where the drivers head in the car would be. Given the game has 1st person perspective views, that might not be impossible to do - but I'm unsure if it's something that could be altered through configuration files, or if the game would need to have code rewritten. I also don't know exactly where that audio is positioned in the game right now. To me the spotter sounds like it comes out all the speakers and isn't really positioned anywhere specific...? It's an interesting idea though...
