Any software that supports "kiss" mode should work with a "kiss" mode TNC. "Kiss" mode is just where the APRS packet processing happens. In "kiss" mode, the APRS packets are processed by the computer, not the TNC. The TNC just acts as a "dumb" modem and the important thing to remember about "kiss" mode is the baud rate between the computer and the TNC is the baud rate that goes out over the air.
this is incorrect.
the op asked about the tnc-x
this tnc is capable of 1200bps mod/demod (radio) only
it is, however, capable of communicating with the terminal @ 9600bps (as well as the rest of the common speed).
depending on the options, the tnc may only have the rs232 port or may have the usb option installed.
while setting up a 'soundmodem' certainly opens up other transmission rates, the tnc-x will always operate 1200bps packet regardless of the speed it communicates with the terminal (computer)
as to the OP:
there are a few terminal programs that will work with a kiss only tnc.
if you are wanting to operate connected mode packet rather than just aprs or other unconnected modes, you might consider a full tnc rather than a kiss only.
your terminal options across platforms will open up significantly.
good luck!