You should be able to use the TS300 with the 4219 zone inputs.
The + and - terminals on the TS300 get connected to a DC power supply of 7 to 16VDC.
The alarm relay outputs are the terminals labeled Output1/COM and Output2/COM. You would wire Output1 and Com to one zone input and Output2 and COM to a second zone input. (I'm assuming you want to use one as a low temp alarm and the other as a high temp alarm).
If you have the TS300 programmed to operate the outputs as normally closed, you would add a 2000 ohm resistor in parallel across each set of Output and COM terminals as an EOLR.
OK. I should have warned you that I'm a novice.
The biggest question I still have is the configuration of the 2 resistors. Is it the same set-up as door closures? On my panel, one wire goes directly to one of the zone terminals, but the other wire is connected to one end of a resistor. The other end of that resistor is then connected to the second terminal on the Vista. Will this be the same?
So, I'll need a total of 6 wires running between the Vista controller and the TS300:
o + and - from terminals 4 and 5 on the Vista (also used to power keypads)
o and 2 pairs wired to 2 zones on the 4219 expansion module
Which would be the better way, normally open or normally closed? I guess normally closed, so that I get an alarm if a connection gets loose?