Ok, I have been looking for 2+ weeks and can't find anything that helps.. I have my Xenyx 802 mixer setup just as above, (except for input 2) but I'm having problems with hearing myself in my headphones. I can only hear myself when I use CD/TAPE to mix (which records my instrumental as well). I had it hooked up this way for 6 months or so and never had a problem with it. Unhooked it for a party, and when I hooked it back up to my computer, it started doing this.

Well , try a few different set ups I'm sure all that is happening is you have moved your cables, I see a few different ways you could wire things in there. 

Or you could return the mix from the computer to a channel 3/4 and pan it left, Then arm the vocal track to right channel.

If you depress CD/TAPE TO CTRL do you hear anything at all through the headphones (with the instrumental tracks playing)?
If not, this suggests the switch may have sustained some damage. We know the signal is getting from the sound card to the CD/TAPE input, because you record the instrument tracks with CD/TAPE TO MIX depressed.
CD/TAPE TO CTRL completely isolates the 'phones from the rest of the mixer.
Is Input Echo turned on in your audio track that you are recording to?
Bases on the  slim clues you have offered, it seems likely that Input Echo is turned of.
What you have written seems to indicate that you have a complete signal path.

If you turn on Input Echo with CD/TAPE TO MIX engaged, you will most likely get a fierce feedback loop until the audio engine shuts down, so be careful with the headphones.



ps. It's good to see my old pic still getting some use.