Stay away from the nad

NAD used to be good stuff.  I am sorry to hear your experience.  Why did NAD not offer to make it good?
I enjoy my 45 year old Crown International DC150A series II   everyday.  Also use a 40 year old Crown SL1  PL1 every day.  Still sounds great.  Both still hit lows hard and clean highs. No service on it since it was purchased. Can anyone beat that for reliabiliy?  It will be fun to hear.  

Apparently Djeng prefers complaining to strangers on the internet to contacting Nad to see if they’d warranty his broken 356. 

Call them.  Get a real live person on the phone.  Explain that you are a repeat Nad customer.  Be friendly.  Have your receipt that proves it's only a "couple of months" out of warranty as you've stated.  Ask if there is anything that they can do to cover this under warranty on a one time basis.  If they say no, politely ask to speak to a manager about this unfortunate situation.  Report back here with the results.

It meant to be advise not complaining. No help from nad.

Sorry for typo. "advice". Yes, I contacted nad and the first question was "is the unit still in warranty". When I said no I've got the answer "Sorry for the trouble". Any further conversation with them was over.

It sounds like you didn't politely insist on speaking with a manager.  It sounds like you haven't pursued the matter, but with a budget of over $4000 for a replacement, you won't miss the Nad.

 I had Denon replace a remote out of warranty.  I've had Paradigm replace a tweeter out of warranty.  I've had Nissan repair my Altima out of warranty.  All free.   I guess perhaps it's a skill one has to develop.