RS5s - upper or lower connections?

If the manual states no difference then it does not matter. Some speakers, like mine, the crossover is designed so that the signal should come in through the lower inputs. It depends on the design of the speaker and the crossover. So if your manual says it doesn't matter, it doesn't matter.
Plug 'em in and enjoy!

That extra set of binding posts is for bi-amping or bi-wiring.

I've never heard of connecting one to the upper and one to the lower though. That's interesting. You hang around long enough you will hear just about everything. :)

Either set of speaker binding posts is fine. Hook up your cables to whichever set is easier to reach and connect. Just be sure that you use the same binding posts on each speaker ! Congratulations on your new speakers. Cue up your music and enjoy !

I'd say the upper set of binding posts. (For the tweeter) Whether you will hear a difference, I don't know. I guess it depends on how long you've been an "audiophile." :)