usb connection for cat and audio…?
Basically, no, you cannot do it all from the USB connector. That is for remote control only.
You have to use a combination of the USB connector for remote control, the speaker out for audio into your PC, and AUX jack or MIC jack for transmit audio into the radio. You can also just use the MIC jack for transmit audio AND PTT for transmit, but you still have to use the speaker out for audio out to the PC. The radio partially emulates an ICOM 7000 for remote control CAT commands (search for ICOM CAT commands to learn about them).
There is no single magic solution, but I’ve made many digital QSO’s on PSK31, Contestia, Olympia, and a few JT65 using Multi PSK, Ham Radio Deluxe (with the embedded DM780 display program).
I initially used the USB cable for getting frequency data to the radio, and the RJ45 MIC jack for PTT and audio into the radio, and speaker out for audio to my PC. i used and old DigiPan MIC adapter. I had to use a 2nd USB-to-Serial adapter since the old DigiPan was serial port only.
A firmware update in late December fixed an issue with the PTT via the USB port. I now use that, and speaker out and AUX audio in.
keep in mind that the audio output jack is a stereo jack. Careful reading of the manual reveals this. (("External speaker output — Speaker or Headphone (3.5 stereo Socket); Otherwise it will damage the rig.... P. 11)).
Therefore, do not use a mono audio plug or the "ring channel" will be shorted out and this could damage the audio output amplifier. Using only one channel, the "Tip Channel," is not a problem if a stereo headphone or external speaker is not used. There is plenty of volume available. This design is to make it easy for using the most common type of headphone out there. Also, since I do not plan to open my radio unless necessary, this is a practical consideration, for me. Photos of the boards make me see in my mind's eye the words, "Don't go there!" Unless something smokes, the covers stay in place.