Your NY reception sounds surprisingly good for an attic mounted CS2. If we were neighbors, you'd see a Winegard HD7698P on my roof, as high as I could safely get it. Going for Philly, I would opt for the Winegard HD8200U.
Both antennas would be equipped with Antennas Direct CPA-19 preamps and cabled separately into the house. I wouldn't bother trying to combine the two sources into a common coax. My preference is to use HTPC with network attached tuners. There are other valid ideas and viewpoints though.
http://forum.tvfool.com/showthread.php?t=820
http://forum.tvfool.com/showthread.php?t=2882