Interesting situation you have.  While I can fully endorse the noise cancelling abilities of my SONY MDR-NC60 headset – I feel they are better at it than the BOSE available at the time, it is an expensive way to go to block out neighbor noise.  The AT line may be as good, perhaps better, but...

Yes, it is "very nice", really.  I have concerns about the tech support...  You sound like you are more knowledgeable than they.  The HD 990 comes with a new and improved DA converter; when I installed it I merely plugged in the optical digital link, I just got it as a replacement for another HK...