Do I need to use a speaker selector?

I have two audio systems. My question is directed to my secondary system, which consists of a pair of B&W 805 speakers (8 ohm, nominal) and a "whole-house" speaker system comprised of 7 pairs of speakers, each connected to a Niles Impedence Magnifying Volume control. The whole-house speaker system is supposed to present an 8 ohm load to the amplifier. I am purchasing a PS Audio GCA 250 to drive the B&Ws and the whole-house system. Here's the question: do I need to use a speaker selector box, or can I hook the B&Ws and the whole-house speaker wires directly to the amp? If I connect direct to the amp, the load it will see may go as low as 4 ohm, nominal. PS Audio claims that the GCA 250 can handle a load with impedence less than 1.5. Am I missing something, or can I skip the speaker selector box and wire directly to the amp? Any thoughts or suggestions would be greatly appreciated.
If I correctly understand that you want to parallel both the Niles box and the B&W's across the amps' outputs; theoretically this should be safe to do with a 1.5 ohm minimum amp load spec. It's a sonic compromise of the amp's damping characteristics, but this isn't a major issue unless performance is the absolute goal, which doesn't seem to be the case in this situation. Be aware however that 8 ohms nominal load can at certain frequencies drop to half or less of that value. Because the impedance curves of the two major loads are dissimilar you should still be within the safe operating area, but DO exercise restraint on the throttle unless the Niles is switched out-of-circuit (no speakers turned on).
Thanks, Bob. I had not thought about the damping factor. But you are right, the whole-house system is more about background music and casual listening. I have a separate system set up for active listening where performance is the goal. A follow up question -- the speaker selector box I have is the Rotel RSS-900. It has impedence protection circuitry built into it. Which do you think does the most sonic harm: using the Rotel Speaker Selector with additional "stuff" in the signal path, or compromising the amp's damping ability by hooking up the speakers in parallel?
Why not buy a cheaper seprate amplifier for the distributed audio. Connecting a string of speakers and the B&W's to a PS with or without the speaker selector box is like using a BMW to do farm work.

For distributed audio you could use the new Parasound 275 amplifier which has a 20 and 40 Hz filter, A&B speaker outputs, and a low impedance switch. This amplifier is really designed to do what you want it to. A cheaper solution would be one of the AudioSource amps. I use them in lots of installations for background music because they are relatively inexspensive and have features that are useful in multi zone aplications.

My 2 cents.
Hmm, don't think I have ever heard the B&W speakers compared to a farm implement. I use the B&Ws in my study and find that they do pretty well when match up to good electronics. I do agree, however, that the PS Audio amp is overkill for the distributed whole-house system. But since I use this amp to drive both the whole-house system and the B&Ws, I want to use a decent amp.
Not knocking your B&W's. The introduction of either a selector box or direct connection of the distributed audio to the PS will have a deleterious effect on teh sound comeing from the B&W's.
Yeah, I suppose I know you are correct. I am just in denial because I want to find a "convenient" solution. Besides, I don't have room for a third amp....or, maybe I do....
Hi Tin it's just a minor issue & I wouldn't worry about it; your main concern is operating the amp safely. When the selector box is switched out (no speakers connected) then your B&W's are being controlled exclusively by the amp, so no compromise exists. When the selector box is in circuit, that certainly introduces some compromises in terms of signal accuracy going to the zoned speakers, but it's only for whole-house background music so don't sweat the small stuff.