I got 5.1 speaker supports with Ubuntu 9.10 as well.

I followed the following steps and got succeeded.
1. Take backup of /etc/pulse/daemon.conf.
2. Edit /etc/pulse/daemon.conf with text editor.
I used gedit tool triggered from terminal as follows
Sudo gedit /edit/pulse/daemon.conf
3. Scroll down to
a. Uncomment it. That is, remove “;” symbol at starting.
b. Change 2 to 6 for 5.1 channels / speaker.
4. Open "alsamixer" by typing same in terminal.
5. Verify surround, LFE are not muted and channels for 6.
6. Restart system to take changes get effect.

That’s it. I got it worked. I saw the change in sound card selection in preference from right click on speaker icon as “ALC883 5.1……….”.

7. Further checked the VLC player output also, by setting 5.1 surround supports in there preferences.

I am too happy with Ubuntu9.10 as it works faster than Ubuntu9.04, got all the necessary softwares like office, KDE, Audacity, VLC player, Virtual box, etc., Thanks to canonical / Ubuntu team.