Replacing one mesh system with another rarely changes the effective range. All home equipment has a cap on transmission power by law, and just about every one of them uses this max limit, as it's very low and extremely easy to accomplish by any manufacturer. They also often use the same chipsets. They do often have different antenna patterns, so you will see some differences here and there, but it will not be drastic.
Rather, you should experiment with the placement of your Orbi nodes. Place them closer together than you might think. Do not place a node directly in a dead spot, but rather in between the dead spot and your main Orbi router. A good strategy is to place the secondary node in the center of your house on the same floor as your main Orbi, or on a different floor, but directly above or below your main Orbi. Often, just changing the angle of attack is enough to change a dead spot into a usable one.
If you're using wireless backhaul, try reducing the number of nodes to the minimum. Most houses only need two Orbi units at most, three for unusually large or weirdly shaped houses.
6 GHz actually has worse wall and floor penetration than 5 or 2.4 GHz, so that won't help you.
Finally, look carefully to see if you can potentially wire in some of your Orbis. If you have coaxial cable or old phone lines, they can often be converted to Ethernet. Doing so will allow you to wire in Orbis in many locations, giving you excellent WiFi coverage.