I suppose that there is a lot of variation in USB sound cards, but I had good luck hooking a USB sound adaptor directly to my UBITX microphone input with a stereo mini jack cable from the headphone output of the sound adaptor. Surprisingly it does not cause the radio to key into the transmit mode with the PTT connected to one of the output channels.
For audio output from the UBITX to the microphone input of the sound adaptor I cut a stereo mini jack cable and hooked the adaptor's microphone input to the ground and high side of the UBITX volume control. The audio from the volume control to sound adaptor microphone input is slightly more than I'd like. I may add a resistive divider to cut the level a bit. I use this arrangement for FT8.
Tom, wb6b
