Are you thinking in terms of a thermostatically controlled system or a pressure balanced system. The type of valve you have in mind would determine which additional valves or diverters would be required.

Going with a thermostatic valve would be the more expensive route, but it has a number of advantages as far as comfort and convenience over a pressure balanced valve.

jamesk...Thank you for your follow-up...Definitely the thermostatic system. I'm just clueless about what we need to order from the homeclick website so when the plumber goes to install everything, nothing is missing.

We've just had some Hansgrohe systems put in our house. Basically, they sell two types of tub and shower valves. One type incorporates both flow control and temperature control. The roughs (the valve assembly itself and the associated fittings) and the trim (the handles, splash pieces, and everything else that is exposed) are sold separately, and you mix-n-match to get the style and capabilities that you want. Roughs are available with 1, 2, or 3 outlets. You select which outlet by which way you move the handle. You cannot plug an outlet and you cannot leave an outlet unconnected, so you have to choose the right kind of rough for the installation. For a conventional tub and shower combo, you'd choose the 2-outlet rough. After it's plumbed, you move the handle to the right for water to the tub spout, and to the left for water to the shower (or vice versa, depending on how it's hooked up). You do not use a diverter-type tub spout with these. For a shower-only installation, you choose a 1-outlet rough.

The other type of valve configuration that Hansgrohe sells is a setup where the temperature control and flow control are completely separate. In this type, you buy a thermostatic control, which controls the temperature but does not have anything to shut off the flow. You can then put one or more flow control valves downstream from it. Our master shower has a single temperature control and then three flow valves for two hand-helds and a rain head. Again, the valve roughs and trims are sold separately.

jdstudio,

If you're going to go with a single fixed showerhead and one handheld with a thermostatic valve you'll need:

1/2" thermostatic valve rough (this is the valve itself, which is the part inside the wall)
Montreux thermostatic trim (the parts you see on the outside of the wall)
1/2" Rough, Trio 3-port diverter
Montreux Trio diverter trim
Montreux wall outlet
Montreux (or other Axor) Hand Shower
Montreux Wall Bar (metal hose is included)
Shower Arm
Showerhead

The Trio diverter will allow one or both emitters to be on at a time. It has an integral volume control.

Alternatively, you could skip the Trio diverter and use two volume control valves to control the flow to each emitter individually.

If you decide to go with two fixed showerheads plus a handheld, and expect to have all three emitters turned on at once, then you should probably go to a 3/4" thermostatic rough to ensure an adequate flow of water. You won't be able to use the Trio diverter with thee emitters if you want to operate more than one emitter at a time. Instead, you'll need to replace the Trio rough and trim with 3 volume control valves and Montreux trims.

With separate volume controls, you can control the flow to each emitter individually, but the water temperature for all three would still be controlled by the single thermostatic valve.

Hope this helps.

WOW! jamesk...Thank you so much for your help. I'll talk to my plumber tomorrow and start to get things ordered. He's been waiting on me for weeks! I truly can't thank you enough for the information, it's exactly what I was looking for. Thanks to you, I'm one step closer to the light at the end of the remodeling tunnel. Thank you, thank you!