Handcraft digital interface

Built a digital interface to work with my KX3, it include
a. USB to UART interface board(FTDI FT232R chip)
b. PTT/CW control port with optical isolation
c. Stereo input to computer for accepting the I/Q signal from transceiver
d. Mono output from computer to transceiver

Option,
integrate the USB sound card(2 in/2 out for SDR application) and USB hub to connect the UART and soundcard interface

DIY the digital interface for digital mode, checklist
a. build-in the sound card - 192K SPS, 24bits, stereo-in/stereo-out
b. build-in RS232-USB interface - 2x FT232R with DTR/DSR/RTS/CTS for PTT/CW keying
c. USB hub function to integrate sound card, rs232 interface
d. signal isolation - 600 Ohm 1:1 transformer for the soundcard input/output, optical coupler for the digital interface. My question - Is it necessary to avoid the RFI in ground loop ?
e. MCU to add more feature

f. study the interface for Signalink USB, Microham, Rigblaster, BH4TDV

For the USB to UART interface board, its output is TTL level and inverse polarity. With FTDI provided tool, the output polarity can be changed.