Years ago, my former housemate would wear both earbuds and circumnaurals when he wanted to play video games and listen to music at the same time. His laptop wasn't powerful enough to run [whatever game he was playing] and Winamp at the same time. He used the earbuds for the VG noises, and the circumnaurals for the music. If you look closely as this shot, you can see he's still got the earbuds in. I got sick of insane amount of sounding leaking out of the music cans as well as him having to take off two pairs of headphones to hear me talk to him, so I eventually built him a rig based around one of my old DJ mixers so he could listen to to two sources with one pair of cans.
That reminds me, do you think we'll ever see an "audiophile" version of that? A headphone amp/preamp that allows the mixing of two inputs at the same time. There has be at least some part of the market that wants to hear video game noises and music from two different analog sources.