Ernest would be your man there I suspect.
The only reason I know about 1-6 is that I sometimes have to work in an office in Uxbridge which is in 6 and so I can use my travelcard season ticket. Whenever I've gone to Watford I've just got a CDR which includes the tube from Vic to Euston.
Indeed. By "travel card" I thought the OP meant the One Day Travelcard that gets you from your station down here to London and then allows unlimited travel on tube, bus and overground. Those only go from zone 1-6. But, yeah, you can do the above.