You are making some confusion here: The F90X doesn't need some Shift button. In Manual the Command Dial operates the shutter speeds and the Aperture is operated by the aperture ring on the lens.
I have always chosen the f/n 80 over the n90/s.
I am ALWAYS in manual mode, and I find it inconvenient to only have one wheel, so that I have to do some shift-button to change time or aperture.
I'm not sure why the F801 does that, but the SB-28 was made for the F5 and F90. I use the older SB-26 and it is perfectly compatible with my F90X. In fact, it was made for them! And yes, the zoom head on the flash does work with my F801.
Talking of which if I use a separate flash on the F801, with a SB28 it will remain on the widest setting, whilst the F80 will zoom in and out as the focal length is changed.