No automount, and HDMI audio issues on Ubuntu Server 12.10

Hi.

I've installed XBMC (from unstable ppa, git20121211-rc1) on my Ubuntu Server 12.10. After struggling with getting it to autostart, I have two remaining issues:

1. USB media doesn't automount. Or rather: USB media DOES automount on the system immediately when plugging it in, but XBMC doesn't pick up on it until more than 5 minutes after I plug in the device. I've followed the HOW-TO from the wiki regarding putting the xbmc user into certain groups and applying a custom policy to it. But that didn't help.
2. AC3/DTS passthrough over HDMI doesn't work; or rather, the bitstream is passed through, but results in screeching static on my TV. Passthrough of these formats works perfectly for both AC3 and DTS with my Raspberry Pi and the same TV.
   

Here's my debug log: http://pastebin.com/rqyHFVSp

In the log I've disabled passthrough, because logging didn't produce more useful info anyway. The HDMI doesn't list AC3 as an accepted format though I know this to be the case (and DTS as well) because the Raspberry Pi builds of XBMC-nightly used in RaspBMC works perfectly.

My hardware and software setup:

CPU: Intel i3-3220 (Ivy Bridge)
GPU: Intel HD 4000
Architecture: x86_64
Motherboard: ASUS P8H77-I
OS: Ubuntu Server 12.10 (x86_64) up-to-date as of 2012-12-20
XBMC: git20121211-rc1 with xbmc-standalone

Test movie: mkv container with 720p h.264 video (works perfectly) and ac3 audio (produces screeching static unless ac3 passthrough is disabled).
Test USB media: Sandisk Cruzer 16GB (automounted on /media/usb0 by the system but ignored by XBMC for at least 5 minutes of the linked debug log).

I'd appreciate any help with figuring out what I've missed or done wrong in order for this setup not to work as perfectly as the RasPi; I can't see a reason why this rig should do any worse.