The Nad amplifier is high quality and probably uses matched transistors that you probably cannot buy.
If these transistors impossible to buy, where does the manufacturer get them?

Anyway, transistors cannot be ideally matched in any case, simply because npn and pnp have different geometry, capacitance, etc for the same current. So, there is always a difference.
If there is a mismatch, the amplifier still will work, at the expense of increased THD. But it's not granted the difference will be dramatic (or even audible). It's also not granted how well they were matched at the factory. Don't you think they buy a lot of transistors and throw away those that are not within 0.001% tolerance?
And, finally, you can match yourself! May be, if you want both channels to be as equal as possible, you may want to match transistors also between channels, but I wouldn't go that far.