I have a SBIG FW5-STX filter wheel with the 65 mm square filters. This filter wheel has a RS232 port on it and works with the same RS232 support as the CFW-10 (you just can only access filters 0-5).
However, if I select this option in SGP from the filter wheel menu, it give me the option for RS232 and I can select a com port. HOWEVER it then simply says it MUST be connected to a SBIG camera, which defeats the whole purpose of the RS232 standalone mode.