Man... something is either wrong with my Surface, or the adapter that I bought. I plugged in a pair of headphones into the splitter in multiple ways. One jack, other jack, both mic and phones plugged in, either one. In any configuration my headphones do not work when plugged into the splitter, but they work when plugged directly into SP3. AHHHHHHH. I'm really sorry, this problem has gone way beyond what is worthwhile to fix. BUT, I have invested so much time and energy into figuring out the WHY's that I have to see this through. It will haunt my dreams and wake me in the middle of the night if I don't fix this... Man has mastered technology, not the other way around. Bare with me. I'll buy another splitter tomorrow and see if it helps.
Edit to add: Just bought this little guy!!!
Hopefully it works a little better....