You could of course see if any of the cards in the graveyard work duplex!
Other than that, it is possible, but most distros won't help you set it up through their GUI interfaces. I seem to remember that Gentoo had some decent stuff on their site about setting up ALSA with more than one soundcard, might well be worth a visit. You would, of course, have to adapt the data for your own computer, but the prociples will be the same.
Asus Asus M2N32 WS Pro+Athlon AM2/4200+ â€” GeForce 7600GT â€” 2Gb Cosair VS RAM â€” 500Gb WD5000AAKS SATA Drive â€” PCLinuxOS