Other than the occasional glimpse of some exotic gear, NYC in general is one of the worst places on earth to look at audio. Unless of course you enjoy being judged by the price of your wristwatch and/or pressured through a high margin sale by a condescending so called salesperson.
In my experience, Innovative Audio is the best of the bunch where Adam in particular is a great guy. But dont know how much used gear they have.
Stereo Exchange used to have a huge stock of second hand high end, but I think in recent years they have morphed into yet another home theatre specialist.
While we are on the topic, I also had a bad experience at Living Stereo, which puzzled me after the intially good reviews. Never went back.
Good luck,
Cwlondon