Is there a digital t-stat that is compatible with this 7-wire unit? I would like to install a Hunter Model 42999B (3 wire with the two jumper connectors Rh and Rc). Is it possible?

Look for a thermostat capable of two stage heat and cool.

A seven wire thermostat for a residence would be a heat pump thermostat with aux. heat strips. If you have a heat pump, ask the people at the store where you purchased it if they have a two stage heat pump thermostat. If you don't have a heat pump then maybe you just have extra wires and don't connect to anything.