Intel MEI is needed for bitstreaming HD Audio with H55\H57 chipsets
Ed Bott's blog on How to update Intel drivers automatically reminded me that I've been meaning to write a blog on Intel Management Engine Interface (MEI) and why you should install it.
I'll keep it short and simple. If you are using an Intel 5 Series Chipset (H55\H57) paired with a compatible Intel Core i3 or i5 for onboard graphics you need to install Intel MEI for HD Audio bitstreaming. You can download it from Intel® ME: Management Engine Driver for Intel 5 Series Chipset-Based Desktop Boards. HD Audio bitstreaming will NOT work without it. A bit frustrating since it isn't well documented and most enthusiasts tend to install the bare minimal drivers to prevent bloat.
The reason why is a little more complicated but basically PAVP 1.5 is a function of the Intel ME firmware that is only exposed when the corresponding interface, Intel MEI, is installed.
There are a few other benefits in Intel MEI but for HTPC enthusiasts that is the primary benefit. This is also not limited to Intel branded motherboards. Intel, Zotac, ASUS, Gigabyte, etc. H55 and H57 boards all require it.
For more on HD Audio bitstreamng, see our guide Bitstreaming HDMI HD Audio Formats from your HTPC.