I have a Quattro 48/5000/70. It has two AC inputs and two AC outputs. I only use one of each. AC input 1 is used for the grid connection. I have mine connected to my mains box (200A service) with a single pole 50A breaker and 50A 6/2 wire. I have the AC output wired to a subpanel with the same 50A 6/2 wire. There is a 50A breaker between the inverter and subpanel. The subpanel has six 20A breakers for powering specific items. I could use the second AC output to power a second subpanel if needed. I just need to keep the complete draw to less than the 5000W capacity. I am not even close to it yet.
The two AC inputs are for example, AC1= grid power, AC2= Generator. I do not have a generator. I have my system configured to use the solar power to charge my batteries, and supply power to the loads. Grid is only used if my batteries reach the low set point of 30% or less. At that point, the grid power takes over and supplies power to my loads only. When solar power is available (daytime), it charges the batteries. When the batteries reach my set point of 1.2% over the low set limit of 30%, the grid shuts down and solar powers the load and charges the batteries. My system has only used the grid three times so far, and only for a short time. It was always around 4AM after two days of total overcast skies, and the solar just could not produce enough power. Once the sun hits the panels, shortly afterwards, the solar would take over again. I love it and it works great. I laugh at power outages now. We are warm, our food stays cold/froze, we have some light, can make coffee and cook.
If I were to have a generator on AC input 2, The generator would power the loads if the grid was down and the batteries hit the low setpoint. I hope I explained that in a way that was understandable. If you are used to the Growatt, this is a little more complicated at first. Once you know how Victron inverters are configured, it is really easy. I will admit that the Growatt is a great little package and very easy to install and use. My Growatt installation had problems with two fridge/freezers running at the same time. My Quattro doesn't.