Wow, this is really getting more complex than it needs to be.

85 db is what Avia suggests because that level pretty much cancels out any ambient noise that might adversely affect the settings. The level you choose is not the issue - the point is that the speakers are all set at the same level.

Set the left front at 0, then calibrate the rest by tweaking the individual speaker adjustments.

Just for giggles, sit down and try it once rather than sit here and wring your hands. It really is pretty easy. If you aren't comfortable with or convinced that Avia is the answer, then use the receiver test tones. How far off can it be, really?