JohnK - I don't think that the formula would apply to the switcher device. It would have to be a bad switcher for it to not run some in series and some in parallel.
I have a 4 way switcher, and it runs some channels in parallel and others in a series. If all 4 are enabled, my switcher will present the same impedance as a single pair (assuming all impedances are equal). Only running 1 and 2 or 1 and 4 give 1/2 original impedance and running 1 and 3 or 2 and 4 give double the original impedance. It's not like mine was of high quality either... It's just some $35 toy I got from a local Rat Shack years ago. I'd be surprised if Forghorn's didn't do that as well...
