I did the same as you did with AlexT's kernel and gladly it has the snd_usb_audio module. Here it also works fine with ubilinux now.
You need no Yocto environment to extract the data from the opkg format. I did it on my pc with Archlinux and wondered that the archive software did know how to unpack .ipk packages by default - really nice.
I copied kernel and modules to the proper places on Edison and finally i did a "depmod" which is important if you install the modules this way.
