With a speaker selector that already has impedance matching, you only need standard volume controls. No need to match twice. You can use these volume controls just fine.
As for speaker recommendations, in the budget range of things, the MAS Audio stuff is the best value and for the better of the upper end take a look at the JA Audio Aluminum Series. 6 1/2″ is the kind of standard size for background listening. If you like it a little louder, then an 8″ would be a better choice for you.
I am planning a multiple speaker installation. I currently have a Monster Cable MSS4 speaker selector but need to order speakers and volume controls. Do I need impedance matching volume controls with this selector? I`ll be using 4 sets of ceiling speakers driven by an 80 watt/channel Onkyo receiver to play CD and FM music throughout my house. Can you recommend volume controls and speakers for this application.