Wyrestorm do a nice 4x4 matrix kit.
4 Input / 4 Output Pro+ (HDBT Lite) Full HD Matrix Switch including 4x RX-70-PP slim receivers - Matrices - Pro+ - WyreStorm - Manufacturer - Habitech Website
This is £845+vat trade.
Control is usually by RS232, and normally once introducing a matrix you want to start thinking about advanced remote control witha processor.
RTI and wyrestorm combination works well, however this is not cheap and you will need to divulge in a little programming. unless you want a remote in every room to change the sources around all the time....
I would personally keep it simple guys, what you have is more than enough.
Mick