I have a quantum gateway and an Apple airport with multiple airport units that I spent a fortune for, but still have poor reception in the far ends of our sprawling home. I presently use both the Fios and Apple networks, and my devices seem to pick the one with the best signal. Can I add the Orbi Triband and run 3 networks?
Running three networks sounds excessive. If you're wirelessly repeating everything, that's going to really slow things down too.
Are you using the Airports for Wireless repeating or do you have them configured as hardwired access points?
What is the square footage of your home, and what kind of construction is it (brick, drywall, wood, alluminum insulation, concrete, etc)?