You can run second instance of Brosix by downloading and starting Brosix portable from http://www.brosix.com/download/windows-portable/. Create a shortcut to Brosix exe with the /multiple switch. Then you need to enter the network number of the different network in the portable instance of Brosix:
Tip: You may want to select a different theme for the second Brosix instance. This will make easier for you to know which Brosix application (IM network) are you using.
To select a theme, go to menu Brosix – Settings – Themes.