You would probably need a good directional FM antenna to get WQXR with it's new signal. I would recommend an AntennaCraft FM-6 aimed at the ESB: it has approx. 6dB gain, and is moderately directional. It should bring in WQXR at those signal levels. However, a lot will depend on the quality of the FM tuner involved.
There are adjacent stations in the NYC area on 105.7 and 106.1 which may cause adjacent channel interference with WQXR,therefore it is very important to have an FM tuner that is selective enough to reject the adjacent channels. I suggest looking at
http://www.FMtunerinfo.com for good suggestions.