I have owned the 170DC and 300DC. The 300DC would seem more impressive given it's WPC and dual power sources, but I prefer the sound of the 170DC. It just has less of a pushed sound to my ears. Much "sweeter" with less congestion. Sometimes more power isn't better... Both are gorgeous, and very good sounding solid state amps, and likely better than anything you can find new at this price point.
With the speakers you have I would use the Klipsch with the 170DC. I would try it without a preamp using the level controls on the front of the unit and in DC mode. Just be careful to have the controls on minimum when starting up. The others would be better served with a preamp in either AC or DC mode. Turn to the 300DC if the speakers are power hungry, 170DC for finesse.