I have just bought a pair of Goldring DR100 rated at 32 ohms for impedance. Would I have trouble driving them with the 68 ohms output rated for the NAD C315. Why would Goldring provide an adapter (screw-on, 6.5 mm) for the amplifier if they would work bad with it?

And.. the impedance of the amplifier must be higher than that of the headphones? Or it's reverse? The C325 is rated at 80 ohms.