03-26-15: MeschYes, ZD has frequently emphasized the criticality of the preamp to the sonics of a system. But one reason for his amplifier-first suggestion in this case might be that the OP's present speakers are nominally 4 ohms, and most likely dip to significantly lower values than that at some frequencies, while his NAD integrated has the same 80 watt continuous power rating for 4 ohms as for 8 ohms (although its "dynamic power" rating for 4 ohms is somewhat higher than for 8 ohms). That being suggestive, of course, of the likelihood that driving low impedance speakers is not its forte.
I like the approach recommended by ZD. I am surprised he didn’t suggest getting the Ayre preamp 1st and use your NAD as the amp until ready to buy newer speakers. I would think he would think it would make the biggest improvement in your system as it currently exists.
While there are always multiple paths to success (and to failure :-)), given the OP's stated preferences and intentions I can't imagine he would be going wrong by following ZD's Ayre recommendations.
Best regards,
-- Al