Blastard,
The FSProject and FSMobile are from the same family of interfaces and use the same drivers. You do want to make sure that both units are on the same firmware version and you may need to flash both of them to make 100% sure that they are. When you do this, only connect one unit to the computer at at time; to flash the firmware. Then power cycle each unit after flashing their firmware. Once you have done this, connect the the FSProject to the computer first and then the Mobile to the Project. Make sure that you are using the power supply for the Mobile and not trying to bus power it through the Project. If you have any other external peripherals connected to the computer, disconnect them and then re-test. Some computers can be a bit underpowered and with extra hardware attached, it can tax the computer's power supply and when the power dips, it can hinder the computer from being able to properly see both units. Additionally, you will want to double check your Recording and Play back settings on the computer; making sure that all inputs and outputs in the computer's audio setting are set to the same sample rate, disable exclusive mode as well as any enhancements that may be active.
Studio One will only see the interfaces as a single Firestudio Device. You will need to configure your I/O in Studio One to reflect the additional inputs and outputs for both active devices.
