First get a Free Cube Simulator for Big Cubes:
Then watch :
Thrawst's youtube 6x6x6 solve
I did the six 4x4 centers first. Build 1x3 strips and insert into centres.
Works pretty much like the 5x5 centres techniques.
Then, I did the quadrages. I paired all quadrages.
For the last two quadrages, if you get the centre 2 edges flipped, use the 4x4 algorithm to correct them:
Last 2 edges:
Last 2 dedges both vertically parallel to each other.
D* R F' U R' F D'*
Then, treat the centre 2 edges as 1 single edge - then you can apply all the 5x5 algorithms to solve the last 2 quadrages.
Solve as normal 3x3 cube.
I encountered 2 parities.
The first parity is a single edge flip parity. I used the 4x4 algorithm:
Parity 2 (1 flipped edge)
With edge in front:
The second parity is a 2 edge swap parity. I also used the 4x4 algorithm:
Parity 3 (Opposite edges - but no flip) &
Parity 5 (Front and Right Edge - no flipped)
With one edge in front:
2r 2U 2r 2U* 2r 2u
Not as difficult as I expected.