it is , you could use linear regulator but the heatsink would be enormous..........
...i presume you mean 6A not 6mA?
....You could use a buck converter, but the duty cycle would be very low, unless you used a tapped buck.
In fact, with a buck you would end up with huge pulses being drawn from the input cap, and high rms cap ripple current..
so a transformer solution would be best......and power factor corrected too at your power levels...........
so what about a pfc followed by a two switch forward for you ?
you can get pfc chips that do both operations...eg LT1509 ........etc