Bridge or bi-amp? Which should I do?

...meaning different amps for each speaker?
If your speakers have 2 or more pairs of binding posts this is a perfect case to biamp your speakers.
On wonder to all other audiophiles I am not familiar with B&W line of speakers.

Unless you are sure that the wattage, impedence, etc. is identical between the two, I'd suggest bi-amping (assuming your 602's are biwirable). Even if their spec's do match, I'd still be hesitant to bride them and run them as monoblocks. I'm guessing that the bridged integrated would not exhibit the same tonal qualities as the bridged solo amp. Just a guess though. A little experimenting would answer your question best. Happy listening.

biamp, so as to not degrade your damping factor via bridging

I would also biamp. I am not sure that NAD amplifiers like to be bridged. Happy listening

I once talked to the folks at Bryston about bridging their amps verses upgrading to higher wattage. They said that when you bridge their amps while you get more raw power, you give up some of the quality of sound (i.e. soundstage, etc.). If that's true of a Bryston amp which is very 'bridging friendly', I wonder if it's not true of most all amps that a person would bridge. I am not an engineer but I followed their advice and went with the higher wattage amp instead of the bridging route. If I were you, I would bi-amp as well.