Replacing original Inverter/Chargers in 2000 LXI

[luckyron1]

I have just installed 6 new AGM batteries. I have the original Trace 3000 watt
inverter/chargers and they seem to be working OK, but, the way I see it, the
failure of the 10 yr. old Trace units is probably just around the corner. The
Trace units are (I think) standard BB installation, stacked, with RC7 remotes
above the pilots seat. I'm looking at the latest and greatest Xantrax unit: The
Freedom 3000 watt, comparing the technical specifications, operations manuals,
installation instructions, to the Trace originals in the Bird Box. Am somewhat
confused, possibly having a brain fart. I hate to ask stupid questions but here
I go.

Why did BB go with 2 stacked inverter/chargers when it appears that just one
would be capable of handling 6 4D batteries? Backup?

If I need two, why? And will they be "plug and play" or will I have to hire
someone to do it? Will one of them have to be configured as a shunt like the
original Trace units? And exactly what is a shunt?

2000 LXI cooling off in MN