I am also on Ubuntu and seeing something slightly different. I've got latest 1.8.1 client vanilla, just installed FML and put this mod in my mod folder. It crashed on me pretty quickly. Tried to check that I wasn't screwing anything up. Here's the crash log output:
I'm on Ubuntu 14.04 and haven't modded Minecraft in 2 years. Apologies for any ignorance on my part for that, but I'm pretty good at troubleshooting and willing to try any suggestions you have or provide any data I can. We're trying to setup a server and would love to have positional audio for all the players. I've seen this work in the past and you've done awesome work. Thanks in advance!