If you have gain controls on your power amps, you might try setting the trims on the 950 to zero across the board, and performing your calibrations with the pots on the power amps. It really sounds like you have a gain structure problem, and the Klipsch speakers are probably pretty efficient. My horns are 106db/watt efficient and the 950 is quiet enough for even these hyper efficient speakers with proper gain structuring.

The "zipper" sound of the volume control when changing volume is normal for electronic volume controls but is undoubtedly being aggravated by your gain problem.