Not that important since only sound but still curious...

A PC work desktop running ScientificLinux 4.1 was at 2.6.9-34 & audio 
(xmms, aumix to control volume) worked great.
aumix showed Vol, Pcm, Spkr, Line, Mic, CD, IGain, Line1, PhoneIn, 
PhoneOut & Video. xmms worked well.
Hardware is Viglen D945GTP motherboard with
82801G (ICH7 Family) High Definition Audio Controller

Updated work PC to 2.6.9-42.0.2 - aumix now only shows Vol & IGain, and no
sound produces - at all! xmms says it's playing - but no sound.
system-config-soundcard says it plays test sound - but no sound.

Rebooted work PC back into 2.6.9-34 - still no sound. At all.
aumix still only shows Vol & IGain.

The hardware has not changed, only the kernel, but then reverting back
does not help. No changes to versions of aumix nor xmms.

What happened to aumix/sound with the kernel upgrade?

Also: brand new Dell Latitude D520 with hardware
"Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller"
On the D520 with SL4.3 (any kernel version) aumix again only shows Vol & 
IGain. However, in 2.6.9-34 xmms plays; in 2.6.9-42, all is silent.

Is there a simple recipe to debug/fix?