Nigel,
I'm not familiar with that particular switch box, but the specs mention that the box maintains impedance at 4 ohms, so you should be alright with it provided you use an amplifier/receiver that will drive 4 ohms without triggering its protection circuitry.
Look at Denon, which here at Axiom, have been very reliable driving the Axiom 4-ohm M80 v3 tower speakers.
Impedance-matching switch boxes do involve sonic compromises, but for your application it should be OK.
For better quality, you could, as my colleague Brent mentioned to you in the private email, go to Russound or Niles for constant-impedance switchers.
Regards,
Alan
