Most of the scales available are TTL, with the exception of some Heidenhain, which can be either TTL or low signal sine wave.
You should only require a marker at one end for zero index.
You may have a problem with 'hunting' if you have any degree of backlash between motor and scale, unless you go with dual feedback, motor encoder AND scale, but I don't recall if the 6 will support D.F.B.
Also I seem to recall the scaling is limited on the 6, so you may need to get compatible resolution scales.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.