By vessel command, are you referring to the Vivid Ux touch screen that controls all of the boat functions? If so, that's made by Medallion. Medallion makes displays and gauges for a lot of marine applications. I'm guessing it's one of their smart displays, because those accept a CAN which is needed for the head unit interface. The problem is that they may not be able to help you much either. I had looked it up before and no longer remember the name of the company, but Bennington contracted with another party to create the GUI and programming for the unit specifically for Bennington.
If you have the Vivid display, your head unit is actually a Rockford PMX-8bb. It's attached to the inside front of the helm and the Vivid display is just a wired remote. The PMX can accept up to 3 remotes. I haven't looked closely enough to figure out if the small Medallion volume knob and stereo control next to the Vivid is a second remote for the head unit or if it wires into the Vivid display and is a secondary control for that. It is Medallion control so I'm guessing it connects to the display, but I could easily be wrong.
Your remote option is the PMX-1r, which is compatible with the 8bb. To run the remote to the rear of the boat, you'd need one of Rockford's 13 pin extension cables. If the Medallion volume control is run directly to the 8bb as remote, you'd also need the 13 pin "y" adaptor to add the additional remote.
I started looking at this stuff before we bought ours because I knew the factory stereo was not going to satisfy me. I've also owned other boats that use proprietary display systems and try to make it a closed system so it's very difficult to modify afterwards. Caveat - I have not done this myself, yet. This is the conclusion I've come to from looking at the wiring and components and doing some research. I've got the PMX-1r and parts, just waiting for the off season to start upgrading.
I think the Vivid display leaves out a lot of adjustability the head unit is capable of. There is the possibility that the added adjustability is there but not visible unless you have the additional upgraded amplifier and M2 speakers though. Once I bypass the amplifier in the 8bb, add amps and a sub, I guess I'll find out. If I don't get the results I'm looking for and can't get support to assist with changes, I'll probably just remove the Vivid display from the loop and run one PMX-1r on the dash and another in the rear.