On my HP Elite 7300 MT with upgraded graphics to a GTX 560TI, I'm running into a pretty specific problem.

I have my audio setup connected to my computer via the back green jack port, but as my system is quite aged (home cinema receiver from the 80's) it takes quite some power and gets quite hot, so I leave it off when I don't want to listen to music. Also, I've got my HDTV connected to DVI port of the 560TI (anyone wondering, yes some cards actually support sound over DVI) since my other HDMI port on it is broken.

When I disconnect my headphones from the front stereo jack when my audio system is off, it automatically switches to the HDTV as a sound output. This is annoying, as I don't always (but sometimes I DO) use the speakers in the TV, and because it is turned off. But now comes the problem, when I plug my headphones back in, it doesn't automatically switch back to the headphones. That is quite annoying, which means I have to change my default playback device every time I connect my headphones.

On my previous Windows 10 box, my Mac Pro 1.1, this problem never occurred to me.
Does anyone know how to quickly fix this? I would have found out the problem myself, that was, if I had that much time, however with school starting next Monday AND having a lot of other computer projects going on, I can't afford to spend time with this too much.

Oh, and another question: I want to combine my front and rear green jack outputs, as I have my speakers turned off when listening to headphones anyway, which means I can turn on my speakers and nothing needs to switch on the computer in order to listen through my speakers.