I love NYC, each year my wife works at NYU in January for a few days and I always go with her. This year I plan to visit World of McIntosh https://worldofmcintosh.com/ that I learned about recently and am very excited about. Other than that, unfortunately you will no longer find any dealers in Manhattan that allow much in the way of window shopping. The guy at Stereo Exchange moved his showroom uptown about 4 years ago - he is nice but best to make an appointment with him. He has very high-end stuff.
You didn't ask, but you can find a good selection of music stores selling records and CD's in Greenwich Village if you're into that sort of thing. Enjoy!