Hi Rock,

This is getting confusing. The NAD C356BEE is an integrated amplifier with its own internal preamp. Why are you using an outboard preamp? Nad electronics are well-designed and there should be no need for an outboard preamp. The latter may be the source of the distortion. You could be overloading the line input of the NAD with the outboard preamp.
How do you control the volume level?
Alan

Alan Lofft,
Axiom Resident Expert (Retired)