I'm no insider, but maybe I can answer your questions.
What Bitrate are they recorded at?
They are most certainly recorded as wav files. I can't tell you which bit depth they use, but I'd assume it's 24bit. The sampling rate should be a minimum of 48KHz since some of these were planned to be released as DVDs as well (DVDs use 48 KHz audio).
Are they recorded through the soundboard?
And finally are they mixed or mastered before release?
yes. The later ones were all mixed by Pat Wilson. The earlier ones were mixed by different people (can't remember any names right now). Please note that these are usually mixed "as it was" in the venue. So errors of any kind are usually not fixed.
The mastering varies. The earlier ones were a lot louder than the new Pat Wilson ones. Don't know if that's good or bad.
That actually helps a fair bit.. I love to hear live music. I'm a fairly big Phish fan. You get a free download with your ticket purchase. So when I saw that the Weez was releasing live shows, I got excited.
So thank you for your reply, I will be grabbing some of the Canadian tour...
Long Live Weezer!