OBS does its capturing per-device, not per-application. You need to use virtual audio cables to isolate sounds like you want to.
You could always "fake" to have more devices with one of the methods I linked you (my previous post), but I guess your solution works too! If it works for you, great.i got it i think
im about to try and use my usb wireless headset for music and plug unused earbuds and use the sound from the earbuds thanks guys for the help :)
but now i have figure out how to do that XD