A question for those with 7.1 systems ... Do you force 7.1 on your amplifiers all the time, even for 5.1 sources, or do you find that a 5.1 source sounds better just from the surrounds rather than 'matrixing' with the surround backs? I'm using a Pio AX10 with two pairs of MA Silver fxi's as surrounds and surround backs. Should I keep the amp set to 'Auto' or always have 7.1? Not sure why, but the AX10 auto setup (using supplied microphone) sets the surround fxi's as LARGE but sets the surround backs as SMALL ?!??!