Just to point out a few things. When you see two gauges on a regulator, one tells the pressure in the bottle, and the other shows the pressure going out to the kegs. What you have is a single gauge that just tells you the pressure out. Most people use something like these to have multiple lines at different pressure. http://www.micromatic.com/draft-keg-beer/regulators-cid-792.html
You can force pressurize the soda, get it at the CO2 concentration you need and then disconnect, lower the pressure and hook up the beer. Just realize the soda will start to go flat as you pull from it until you recharge it.
Leaving both connected at 30psi will turn your beer into foam baths within a couple of days.