You do have the MPPT controller that works now doing 25v, so you just need to get the Xantrex to charge at say 28v into the MPPT and leave the MPPT set at 25.
It would involve some kind of switching so you are on inverter but not charging from the inverter/charger when on solar (charger off/ disabled/whatever they call it).
You can have the input to the controller be either panel or inverter/charger (one of those 1-2- except not both! switches? or just use parrot clamps to one or the other) and the controller is already on the- battery so that stays there so no issue like Mr Wiz mentioned with disconnected battery from controller.
Be a wiring job to where the controller is, or move the controller too, but no new equipment. Just new procedure.
