I would go to an actual plumbing supply store. Tell them what functions, finish, and budget and they will assemble you a system. You could do that in any brand from moen on up. I’ve never sold signature hardware so can’t comment on it.

I'm not even clear what "Signature Hardware" is. My impression from their website is that they are not a manufacturer.

To echo the post above, I'd suggest that "the stuff behind the wall" -- that would be very expensive to replace because you can't do it without a complete re-do of the shower -- should be a company with a well-known reputation.

Don't get too enamored with complex multi-head shower systems. Simple can be good.

I like the functional clarity of the Grohe control valve - I think it looks good also. Others can comment on the quality and such. This is an example of a 3 outlet thermostatic valve - but it's not the only configuration. Like most of these - it uses a common base with various trim / finishes to match your style.

FYI, if you are in CA you can not operate more than one shower fixture at a time. You will need a diverter to direct water to one fixture or the other.