After much searching, I've come to realize I'm not along in in having problems with front panel audio jacks and Windows 7; most related to jack sensing. I haven't seen anyone mention the particular problem I'm having though.
I'm using a Realtek ALC861 HDA codec (with latest drivers direct from Realtek as of today) connected to an AC'97 front panel (not ideal I know). Obviously jack detection won't work with this setup, so I check the "Disable front panel jack detection" in the Realtek control panel. In Windows XP, this worked as expected, always sending audio to the front panel headphone jack along with the standard speaker output at all times. Enter Windows 7.
Now, even when jack detection is disabled, the headphone jack doesn't "normally" work. However, it will temporarily work if I enable and then re-disable jack detection *while* I'm already playing music (in WMP12, say). At this point everything will be working as expected, right until I try to pick a new song to play, at which point the headphones stop working again! Go figure, right? As long as I don't manually try to skip to a new song, it'll continue working until I hit stop. Now of course the details on how WMP manages its audio interfaces aren't really relevant here. What is relevant is that as long as the audio system is active (some kind of sound is coming out of the speakers), the headphones will continue to work. So, for example, if I fire up iTunes while WMP is playing and start playing music in iTunes (with the volume turned down), I can use WMP however I want without losing the headphones. (This is basically my round-about solution to this problem for now .) Oh and btw, this affects all sounds, not just music.
At this point, I don't expect that a solution to this will be forthcoming, so I really just want to know if anyone with a similar setup experiences this as well? I'm tempted to get a proper HDA jack and then use jack detection, but I'm afraid the problem might be deeper than that, especially considering the headphones don't show up in the list of audio devices, even when I tell it to show disconnected devices. To me that implies that jack detection (and consequently output redirection) are handled entirely by the Realtek driver. If I can determine I'm not the only one with this problem I'll try to forward this post to Realtek and maybe get it fixed. Otherwise I guess I'll just pick up some USB headphones and be done with it!
AMD Athlon 64 X2 5200+ (2.6/2x1MB)
Biostar TForce 550 (nForce 550 + Realtek ALC861 HD audio codec)
4 GB DDR2-800
Windows 7 Home Premium 64-bit