I have an 8 Gen 2 on the console and a 8 Gen 1 on the front. All networked up.
Have fuel flow, external temp for the water, external temp for the air, side scan, 4 K GPS puck, and engine adapter on the network.
If I strike it rich or do a good job saving, I will move the HDS8 gen 2 to the front and get a HDS touch 9 for the console.
All the HDS has it's own internal antenna and you can switch back and forth or set it up as you want to.
Shoot me an email or a facebook message if you want any more information on my setup.