I caught another handoff here in Cape May Empire 11 switched from ZDC51 Casino 285.400 to ZDC39 Snowhill 236.8250. I looked in up on Ron's list and its an aircraft out of Oceana Air Station in Virginia
There is also some army helos that use the ID EMPIRE that transit through NJ on a regular basis. But being you heard the handoffs on those ATC channels, it probably was a fixed wing.
Justin - can you hear the controller on 127.700 Washington Center freq? If yes then monitor that when there is activity on 285.400 and you will at least hear the controller side.
Thinking back to remembering the activity on the radio - they were definitely fixed wing aircraft.