need advise on how to proceed with wiring a Lionel 6-5906 to FastTrack using my ZW 275 watt train master transformer.
See the Lionel information sheet here:
Since you are using FasTrack, where the diagrams show a wire going to the "2" terminal on the tubular track lock on, that goes to the wire connected to your outside rail. the wire shown going to the "1" terminal goes to your wire that is hooked to the center rail.
(I'm making the assumption you already have the track hooked up to the transformer in some way)
Use wire nuts or screw terminal blocks to connect the wires, whatever you are more comfortable with. (or you can always twist and solder, if you are proficient with a soldering iron)