If you are still having problems try theses commands to collect more information.
# lspci
00:00.0 Host bridge: nVidia Corporation MCP79 Host Bridge (rev b1)
00:00.1 RAM memory: nVidia Corporation MCP79 Memory Controller (rev b1)
00:03.0 ISA bridge: nVidia Corporation MCP79 LPC Bridge (rev b2)
00:03.1 RAM memory: nVidia Corporation MCP79 Memory Controller (rev b1)
00:03.2 SMBus: nVidia Corporation MCP79 SMBus (rev b1)
00:03.3 RAM memory: nVidia Corporation MCP79 Memory Controller (rev b1)
00:03.5 Co-processor: nVidia Corporation MCP79 Co-processor (rev b1)
00:04.0 USB Controller: nVidia Corporation MCP79 OHCI USB 1.1 Controller (rev b1)
00:04.1 USB Controller: nVidia Corporation MCP79 EHCI USB 2.0 Controller (rev b1)
00:08.0 Audio device: nVidia Corporation MCP79 High Definition Audio (rev b1)
00:09.0 PCI bridge: nVidia Corporation MCP79 PCI Bridge (rev b1)
00:0a.0 Ethernet controller: nVidia Corporation MCP79 Ethernet (rev b1)
00:0b.0 SATA controller: nVidia Corporation MCP79 AHCI Controller (rev b1)
00:0c.0 PCI bridge: nVidia Corporation MCP79 PCI Express Bridge (rev b1)
00:10.0 PCI bridge: nVidia Corporation MCP79 PCI Express Bridge (rev b1)
00:15.0 PCI bridge: nVidia Corporation MCP79 PCI Express Bridge (rev b1)
00:16.0 PCI bridge: nVidia Corporation MCP79 PCI Express Bridge (rev b1)
00:17.0 PCI bridge: nVidia Corporation MCP79 PCI Express Bridge (rev b1)
00:18.0 PCI bridge: nVidia Corporation MCP79 PCI Express Bridge (rev b1)
03:00.0 VGA compatible controller: nVidia Corporation ION VGA (rev b1)
05:00.0 Network controller: Atheros Communications Inc. AR928X Wireless Network Adapter (PCI-Express) (rev 01)
# cat /proc/asound/cards
0 [NVidia]: HDA-Intel - HDA NVidia
HDA NVidia at 0xfae78000 irq 20
# lshw -C sound
*-multimedia
description: Audio device
product: MCP79 High Definition Audio
vendor: nVidia Corporation
physical id: 8
bus info: pci@0000:00:08.0
version: b1
width: 32 bits
clock: 66MHz
capabilities: pm bus_master cap_list
configuration: driver=HDA Intel latency=0 maxlatency=5 mingnt=2
resources: irq:20 memory:fae78000-fae7bfff
# cat /proc/asound/card*/codec* | grep Codec
Codec: Realtek ALC662 rev1
Codec: Nvidia MCP7A HDMI
For the list of alsa Models
http://www.kernel.org/doc/Documentation/sound/alsa/HD-Audio-Models.txt
Choose the model and then try the different model options until you get it working the way you expect it to.
Example:
Edit /etc/modprobe.d/alsa-base.conf and at the end put options snd-hda-intel model=6stack-dig or what ever model you find that works for your sound card.