You are mixing apples and oranges. A 'TNC' is a Terminal Node Controller and used for AX.25 Packet only. . . such as Packet WinLink. Kantronics was one of the main manufacturers of TNCs. . Also, there is software that will work instead of a TNC hardware unit ... such as the UZ7HO program. The other devices you mention are Sound Card Interfaces .. the SignaLink, Rigblaster, and others. These are not designed for packet radio, but for most other amateur digital modes. If your radio already has a sound card in it like my IC-7300 does, you do not need an interface for most digital programs. Just connect your computer ( with the appropriate USB Driver for your radio already installed) to your radio with a USB cable. Then you can work most WinLink HF modes, ARDOP, VARA HF, etc.