just to give you some info. i also have a vortex sound card and i have found that it is best to d/l the cvs version. you can do it this way:
--open a terminal
cvs -d:pserver:firstname.lastname@example.org:/cvsroot/aureal login
--press enter at the prompt for a password for anonymous use
cvs -z3 -d:pserver:email@example.com:/cvsroot/aureal co aureal
i believe that this is a dead project so you will have to open the Makefile and change some things. the one thing that i have had to change is when the make file searches for your hardware. it will be the line that looks like this:
ifneq ($(shell /sbin/lspci -d '12eb:3'),)
NAME = au8810.........
what you will have to do is after the driver d/l's you will have to find lspci by using "locate" then change the line in Makefile accordingly.
after this then:
# make install-all
here is a link to the readme in the cvs version:
where it lists your card as "au8810"
now i am not sure that this will work with MDK 9.1. i got the same result as you but i was back on the verge on distro experimentation (which i am almost done stopping with debian) so i didn't try too hard to fix it. this looks like it will take some research and hard work to get it working for you or you can go back to MDK9.0 where i know it worked using au8820. now i am not saying that MDK9 will work perfectly but it does give you sound. let me know how things go.