We are installing a walk-in shower. On one wall we'd like to put a handheld shower & on the opposite wall a stationary shower head. We'd like to have separate controls for them on their respective walls. We're going to use Grohe shower heads....#1 should we use 1 or 2 valves? #2 Should we stick with Grohe valves or could we use a universal valve like the Delta R1000? Thank you for your advice.