As far as i know, M15HD2 is only released in late 2011 and many dealers dont get the stock until beginning of 2012..how could you have sold the HD2 version to your customers for a few years? Perhaps you're talking bout the HD version instead? For those units you have sold and running fine, consider yourself lucky by not having your customers breathing down your throat over repeated failures should they have gotten lemon units in the first place. I wont have swear on them if i were you because anytime if any of the lemon units were sold through you, you'll biting your own words and only then you know what's the sheer frustration i am talking bout. Anyway, I got my sets directly from Lenbrook outlet as factory A stock.
Just google around and the reliability issue on NAD is all over the place..it's not my intention to bad mouth the company but as a real owner owning NAD gears, i can vote to say that their products dont seem to perform consistently from time to time and durability wise it's also questionable. Mind you, i splashed over $10k worth of NAD Master gears which said a lot of my initial confidence with them but imagine if you're to spend such amount and got such treatment, what'll be your reaction then?