Hi Juladi,
welcome....maybe I can help you.
First: You don't have to change your aspect ratio from 4:3 or 16:9 to for example 3:6
Almost every LED wall has a controller which is connected between your Video Output and the wall.
Resolume Video-Output --> LED controller --> Wall
Ask the LED-wall guys what type of wall they are using and *important* how many pixels every LED module has.
For example:
They are using 1x1 m modules with a 10mm pixelpitch. That means that there are X = 100px and Y = 100px on each module.
The entire wall is 3m x 6m...so you would have 300x600 pixels where you can place content. Now you have to choose your video output resolution. 300x600 fits in 800x600 which is a standard 4:3 resolution.
You can use VGA. But if you and the LED Controller has the possibility to handle DVI you should use a MiniDP-Port to DVI adapter.
The LED-Controller configures all the LED modules to "look" on your defined content region in your output.
I hope that helps?
Here.... a pixelmapping from my last job so you see how it also can look like.
LINK TO PICTURE
Greetz
cosmowe