There is a guy on youtube that amp dynos a lot of products. A pretty fun channel to follow.

He has tested 2 older Nad amps. Both pretty much doubled their rated output and had quadruple their rating in dynamic power.

https://www.youtube.com/watch?v=CA582cvAfjA

https://www.youtube.com/watch?v=KK7xss_IcSg

That being said they are built to a price like anything else. If you really don't want to wonder I would say go ahead and buy the Axiom amp.