Yes. AVR that have preouts allow you to connect an additional amp.
AVR are not "whatever by X" in real terms. The 7008 is not a lightweight, at all. But it only has "so much total power" to devote to audio. When you divide that by 7, you get less per channel. If you take the main two speakers away from the AVR, it can devote its power to center/surround.
The PS S2 is 88db efficient(or 91 room)...which is the same efficiency as the S6.
The amount of power you need for the room is up to you and your listening style.Go to the full post