Re 'kill'. Sorry to hear that.
Using a software modem aka SoundModem by UZ7HO is much more rewarding. It also decodes many more packets than a regular TNC (see the DireWolf manual on how this is achieved). AGW is also there.
You have got to install SoundModem preferably on your APRSIS32 PC and ditch the TNC. The Audio to/from radio now goes through the PC soundcard , PTT via RTS or DTR with the help of a serial port. Other variants are also possible, SignaLink, external or rig soundcard etc.
Re KISS, https://www.scc-ares-races.org/data/packet/docs/NOSintro.pdf pages 39 (44 in the PDF) and 42 (47 in the PDF) can shed light upon the matter.
73 de J