nvidia-driver-319-76 and no surround HDMI audio

[te36]

6 channel PCM HDMI audio via NVIDIA GeForce 210 breaking after upgrade.

1. OLD: Running system

Portage sync'ed end of 2012. gentoo-sources-3.7.4, nvidia-drivers-313.18, xorg-server-1.13.1.

Start "Xorg" server. Run: "speaker-test -Dhdmi:CARD=NVidia_1,DEV=0 -c6 -twav"
6 channel sound working nicely (*).

2. NEW: Upgraded whole gentoo last week, "emerge -uvpND world, etc. pp". Still using gentoo-sources-3.7.4, but now nvidia-drivers-319.76, xorg-server-1.14.3-r2.

Reboot (nvidia-drivers-319.76 installed)

Xorg ; speaker-test ...
-> 6 channel surround sound NOT working (only stereo channels). Receiver shows "PCM HDMI"

emerge =x11-drivers/nvidia-drivers-313.18 ; modprobe -r nvidia ;
Xorg ; speaker-test ...
-> 6 channel surround sound works (*). Receiver shows "PCM MULTICH HDMI"

emerge =x11-drivers/nvidia-drivers-319.76 ; modprobe -r nvidia ;
Xorg ; speaker-test ...
-> 6 channel surround sound works (*). Receiver shows "PCM MULTICH HDMI"

reboot ; Xorg ; speaker-test ...
-> 6 channel surround sound NOT working (only stereo channels). Receiver shows "PCM HDMI"

Aka: After you've started a 313.18 driver and then change over to the 319.76 driver, that 319.76 driver will also work. Looks/sounds to me as if the 319.76 driver is missing? some initialization that the 313.18 driver is still doing correctly.

Q1: Does anyone have working 6-channel surround-sound with 319.76 and an NVidia G210 ?
In NVidias web-page, 313.18 mentions the G210 as supported, but 319.76 does not lists it anymore, so it could be that NVidia explicitly removed support for it.

Right now i am sticking to 313.18, but the driver already complains about the 14.1 xorg-serer and API, so i would really like to resolve this issue:
(WW) NVIDIA: This server has an unsupported input driver ABI version (have 19.1, need < 19.0). The driver will continue to load, but may behave strangely.

Q2: is there any gentoo live-DVD that has 319.76 so that i could try to boot that live-DVD and see if it works better ?

Q3: why is (~)313.18^s[1] marked as unstable, if NVidia lists it as a verified driver (and if it's officially the last one supporting the G210 which AFAIK is quite popular due to being passive and therefore ideal for linux-STBs/XBMC).

Q4: anything else i should try to figure out this issue ?