Good to hear that the 705 and 7610 are working OK for you.
Regarding the USB connection, audio over USB is only really used for the wfview server, the reasoning being that if it is connected over USB, the computer is likely next to the radio so you can either use the radio speaker or if using datamodes, you can just select the USB audio devices within your datamodes software.
Once the server portion is enabled, then if you have selected the USB audio devices for your rig within wfview, this audio will be sent to a remotely connected wfview. In the v1 release, this was quite experimental but we have made significant progress on the server side so will soon be releasing a 1.1 version.
As far as the 9100 is concerned. There is no specific support for it but as long as it uses the core Icom command set, it should work. Band buttons and any additional modes that aren’t common to all rigs won’t be available though and you will need to manually enter the CI-V address.