Soaking tub on the second floor: safe?
If what you're saying is the tub will be on top of 2x10 at 16" on center spacing, with a span of 9 feet between bearing points that continue down to the foundation, you'll be fine. A drawing of the complex framing you seem to have would help out immensely. I still recommend doing the drawings and getting permits: I have a lot of experience framing houses, but I'm not an engineer. You can find span tables online that can help you determine weight allowance for framing members. 

FYI, the 'average fill' is probably based on the displacement of two people in the tub; even if you could fit more water in, you'll probably want to only fill it halfway before two people get in.