If you don't put more than 2 speakers on each channel of the amp then you won't need any impedance matching in the system.
Worth saying that Pyle is a pretty low-end manufacturer, so any use of their products should be considered along the lines of being able to live with it failing, introducing noise into the system, and not working as expected. I would consider AudioSource over Pyle. Still, their Hybrid Pre Amplifier looks like it would be fine. I would not personally connect speakers to it though.
Yes, you can put volume controls wherever you would like and it shouldn't be an issue. If it makes things easier to not have them in the wall, but in a 6 gang back box in a case of some sort, that should be just fine.