LiveCD mode with persistant is not particularly efficient as it's using a form of overlay file system. Easiest and probably best way is to use two USBs.. Write the Live CD USB to one USB, and the insert both USB into the PC you want. (Make sure you set the BIOS to boot from the correct USB).
Now get into POST, and Snakeoil OS Live CD mode should boot up, install the OS directly into your second USB stick. And it should work from then on. This should be what you did with your USB SSD before. And in theory SSB should have better audio quality than USB stick.
Can you take a picture of the error after you did apt-get update?