Which thermostat for both forced air and baseboard heating
The W2 (Aux/E) terminal on the thermostat is for a second stage heat relay or heat pump auxiliary / emergency heat.  

Note that this is to energize a relay or contactor coil, which will in turn energize your baseboard heaters;  you can't directly switch baseboard heat with the Honeywell 9000.  

Selecting a contactor or contactors and rewiring your baseboard heat so that it is controlled by the smart thermostat rather than the line voltage thermostats you're using now could be an easy job, could be a hard job, depends on the existing wiring.