Your UPS will likely top off your AGMs and hold them at a high (float)voltage that will keep
your solar PV controller from ever turning on. But the Xantrex has an adjustable float voltage..
The problem with cranking it up, to use the PV, might be excessively high float voltage.
You might want to put the UPS AC power input on an SSR, that is controlled by the amount of sun available.
That would give the solar a chance to work.
When you wanted to use the chargers to charge up a discharged bank or motorcycle, both sources should feed power in,
while the pack voltage was low..
My backup system is doing nothing these days, but staying in
float all day long..
500w of tracking PV array going to waste..
Wish it was running a GTI.. But that would be illegal..