Multi-room audio system (speakers & Amp question)

[dwalter]

I recently hooked up inceiling speakers, and box speakers in a pre-wired home. I would like to use 2-sets of inceiling speakers, 1-set of box speakers and eventually 1-set of outdoor speakers.

Here is my equipment list:
-Amp: Onkyo 120 watt 8 ohm
-Inceiling speakers: JBL HTI6C (2 sets)
-Box speakers: Infinity 8 ohm (1 set)
-Speaker selector: Sima SSW-L4-EX (4 speaker unit)

Here is my problem: I can't seem to use all three speaker sets at the same time. The inceiling speakers work fine until I attempt to turn-up (turn-on) the box speakers. As I turn up the volume (past 0) on the box speakers, the inceiling speakers lose all volume.

Does anyone have any suggestions?