... I saw MotorOutputs tab there is 6 axis setting available... but in Mach interface I see only 4 axis indicator...
Mach will control up to six axes.
What you see on the screen is purely a function of what the screen designer wants you to see. Each button, DRO, LED can be displayed or not as necessary.
If you want a six-axis screenset, you have to design/write one.
Have a look at the customisation manual for a list of items that are possible (UserButton, OEMDRO, OEMLED).