There has been no suggestion -- it's just a hard fact. 6000XP can't back-feed the grid.
No one knows the details of your setup, no doubt what you want to accomplish is possible, but the 6000XP isn't going to be part of feeding anything back to the grid.
The 6000XP cannot invert battery energy to AC power when in Bypsss Mode (hence the reason it is a off-grid inverter), but is there anything in the manual or specifications stating that it will prevent excess energy from grid-tied inverters connected to the EPS Output (Critical Loads Panel) from passing-through the Bypass Relay when the inverter is closed (inverter in Bypass Mode)?
I’m not recommending this nor saying it will function in this way, just clarifying that Off-Grid inverters are ‘allowed’ to pass-through excess AC power from grid-tied PV inverters to their AC output (while not being able to pass out any AC power the inverter itself generated from battery energy) and also pointing out that the manual is silent on this entire topic.
The Conext SW is an example of an off-grid inverter that allows excess power from grid-tied inverters on it’s AC output to export out if it’s AC input:
https://www.se.com/us/en/download/document/SW-NA_OG_975-0638-01-03/
Look at the section on ‘AC Couple Smart Charge’ on page 1-14:
‘As long as the battery is able to accept the energy, the Conext SW will continue diverting excess PV production to the battery.
Once the battery bank is at a level such that not all excess energy from the PV Inverter is being absorbed, the balance will then flow out to upstream loads in the house that are not connected to the Conext SW’s AC output port.’
Of course, the Conext SW was one of the first Off-Grid inverters to support AC Coupling and the manual is full of sections describing how to use AC-Coupling, so I’m not saying the 6000XP will function at all like the Conext SW when AC-coupled PV is connected to the AC Output (EPS Output).
I’m just pointing out that Off-grid Inverters are ‘allowed’ to pass-through excess AC power coming from grid-tied PV connected to the AC Output (as proven by the Conext SW).