Interesting problem.. not sure how to fix your particular case, but I have a working distribution with libasound2 so it will work in the end! You may not want to follow my yocto route, but at least it can give you hope that you can solve the issue. Things to take note of:
1/ fpga needs to be correct to get sound working with hdmi cable - my yocto environment uses the latest oh fpga code and a "special" epiphany driver.. the official one is in progress.
2/ my yocto environment builds the whole distribution so you should expect to leave the computer building stuff for a few hours depending on the speed of your machine.
3/ I am using ADI kernel 3.19 patched with epiphany driver, the next official parallella one that supports oh fpga is likely to be 4.? so I am soon going to update the kernel and at the same time likely pick up the official parallella kernel / epiphany driver, so the yocto environment will be changing soon!
If you want to have a go the getting started guide linked from viewtopic.php?f=49&t=3180&start=10#p15756 will give you an idea about what you need to do. The environment is at https://github.com/peteasa/parallella but you will find has lots of submodules to fetch. The linux distribution is build from within the parallella/parallella-yoctobuild folder so that is the minimum you absolutely must fetch.