I was also hoping to find a way to do this, I'm really disappointing that it seems impossible in Mac OS X.
Even worse I've just been playing a game in Windows 7 in Bootcamp on my early 2011 iMac and was able to plug a headset into the mic and headphone sockets and use the headset for vent chat AND use the speakers for game sound so its not hardware (at least on the latest iMac).
I reboot to OSX and I cant even flick between the two outputs without unplugging
Now if only i could get my bluetooth headset to work in Windows as easily as in OSX I could have one setup for both and it wouldn't matter!
I'm afraid that's not true. In Mavericks/Yosemite plugging an external device into the headphone jack removes Internal Speakers from the options in the Sound Preferences pane.
I'm afraid that's not true. In Mavericks/Yosemite plugging an external device into the headphone jack removes Internal Speakers from the options in the Sound Preferences pane.
I had same issue with an avionics headset.
My solution was to get a USB headset/microphone.
I have powered speakers running from my headphone out, but I could easily use my built in speakers instead.
This allows me to have certain conversations on the headset, while listening to music/system sounds through external (or built in) speakers.
Depending on the application, MOST will honor the pref to chose input/output WHEN they are started.
Some will change on the fly, some will not.
You can then change it back after application launches.
TLDR:
Spend $10 for a USB adapter available from any online mega retailer. Just search "Plugable USB Audio Adapter with 3.5mm Speaker/Headphone and Microphone Jacks".