Don’t overlook the importance of resistor tolerance. The difference you hear may be (probably is) variance in actual resistance affecting the ability of all circuits in the signal path from meeting the designer’s objectives. Subtle variances can be cumulative and substantially different between left and right channels to skew imaging across the spectrum in non-linear fashion. For these considerations I move that using 1% resistors should minimize the above variances significantly more effectively than the nuances of exotic metals or compounds.
