Save the money on the external amp and just run wires from the B-channel of the RR2150. It's designed to run two sets of speakers at the same time.

But read the addendum for restrictions on driving two sets of speakers.
_________________________
975/7075/SMS-1
Aperion Verus Grand Towers & Bookshelves, Verus Forte Center, Infinity Surrounds, Ultra-X12
Oppo BDP-203, XBOX360, Xbox One
LG 65" OLED
RR2150 w/Klipsch SCR-2