Batboard

I seem to recall that in years past it was possible to have a dual control radio setup with different control heads in front and rear, however there were some limitations. Does anyone know what will and will not work? I currently have an APX8500HP with 09 control head in the front with siren and URC and want to add a rear head...preferably NOT an 09. Have O5, E5, O2 and O7 options available.

Thanks

Mike