If i purchase the Pioneer SC-LX81 amp will i notice a hell of a difference on my 600 B&W surround speakers im using 685s front and rear with an onkyo 605?
Very much so. Every aspect of the sound will be improved. It should be much cleaner and accurate with better placement of effects. There will be less of a front/back sound and more of a whole soundfield. In 2ch the differences will be very marked.