Hi Folks, my final thoughts on the discrepancies I was noting with the sound depending on which side was connected.
Ran the tests ballrd3 suggested but everything seemed fine from a technical point of view (left/ right balance, bass, treble, voice phase etc).
Finally it comes down to the tonal character of each connector. I no longer say that the right side is defective, it just has more headroom and is more open and room feely while the left side has a more closed signature as a classic closed can has. In fact I'm preferring the right side now, particularly with jazz recordings which sound live and have that being there feel. ( listening to Charlie Haden' private collection as I write this)
So take a pick of the following:
1) I have super sensitive ears
2) the connectors somehow are burn in sensitive, and/or NAD is using a crossover or some such to create the room feel....basically that there are other components between the sound signal and the speakers which introduce anomalies.
3) I'm imagining things and should stop this and get a life! ( ok, scratch that, I'm definitely not imagining this.....!)
Anyways, like I said before, I'm keeping them and I hope I've created enough ripples here for everyone to run their nad's thru some tests of their own!