I used 6 basses on our last recording sessions, 4 were different P-basses though (black nylon strings, flats etc). I used a Rickenbacker on one track & upright on the more rootsy stuff (that actually wound up being held back for the next record). I believe too that you should listen to the engineer as (s)he does know the studio best BUT also agree, yes, you are the paying customer. I'm afraid I'd only follow Lozz196's advice if you had no worry about the budget. Bass tends to have the least input on recordings (sadly with vocals ironically so often being overlooked too - on demos at least) so it's best to just know your chops and get the part down as quickly and as best you can. Quite often tones can be fixed in the mix more too