After a long time I've got it working now.

Uninstalled TS and removed all leftover files (User/appdata and Program files). Reinstalled TS (64 bit) and TARS (64bit).
I think the 32 bit TS version was the problem.

To get the L/R settings working, you have to alt tab out of DCS to re-enable the TARS plug-in in TS.
So the first thing to do in the cockpit is "alt tab" to TS--> settings-->plugin-->and check "off" and "on" the TARS plugin.