Any Plumber out there ?

It's called a pressure balancing loop. Here's a link to a drawing. Google images of more if you need to. Good luck with the project.

http://images.google.com/imgres?imgurl=http://www....

Edit; the theory is the same whether there are two spray heads or ten. You will need to arrange the piping so that the water pressure will be consistant at each spot. If you are using control valves (to turn sprays and showerhead on/off seperatly) you will need to pipe them in a similiar fashion too so the sprays and showerhead get equal pressure.

I think you're fitting an anti-syphon valve - so the loop isn't necessary. It's just to stop the shower head from sitting in the bath. If a valve is fitted - it doesn't matter.

The problem is - if your shower head was in a bath of soapy water - and the water pressure dropped - it could syphon dirty water into the clean mains water.

Non-return valves are a requirement for outside taps - but frequently omitted.

The truth is that nobody can answer this question honestly.

1st. Without knowing the manufacturer, and model, to offer assistance would be futile.

2. What kind, or type, of feed lines are available to the unit?

3. Without being aware of the overall pressure for the home, and what's available to the unit, anyone would be less than honest if they attempt to answer this question.

Feel free to write to myself. Give me the manufacturer and model. I probably have the specs here to send or describe to you. I will offer all my best advice and assistance to you. I have installed many of these units and can offer some good insight(s).

keeping the pressure even is what it is all about; you should have two shower heads on one side and two on the other side, they will all be looped in off of the center main feed water line