Since the bulk of your equipment is Extron then the easiest solution would be any of the many Extron touch panels, keypads and/or processors.
You could get an Extron processor with the correct amount of serial ports and control it with an iPhone or Android smart phone or tablet. Or, you could use an Extron wall mount or desktop touchscreen as your interface.
Extron makes in-wall keypads which send RS-232 codes to your devices. The drivers (software code) would already be written for any of the Extron products. Adding the other products would be a piece of cake. With your equipment list, and depending on what type of control you want to have, you may need several keypads.
You have to decide which interface works best for you in this system you're putting together. But by using Extron products you will really make the process very simple.
Take a look around here:
[Link: extron.com]and here:
[Link: extron.com] (select the tab for Diagram)