Most studio engineers will tell you to set the bass flat.. and for good reason. Any half decent studio will have outboard EQs that will do a much better job than an (comparatively) cheap onboard eq on a bass.. not to mention that EQing is usually done in the mixing process, not as common to see someone hit an EQ on the way in (for obvious reasons).
Don't worry too much about your gear, just make sure your basses are setup well (and perfectly in tune, check before each take), play simply, concentrate on time, and you'll be fine
Also;
- take the time to get a good monitor mix in your headphones, and don't be afraid to speak up if you want your mix tweaked.
- take a notepad, and jot notes in between takes
- keep it simple
- stay hydrated
- be open to suggestions on the day.. and considering you already have the demos, work on a few different groove ideas for each tune.
thats about it, good luck! i love studio gigs, can be a lot of fun.