May I please know if we can add 2 dual extruders to the Lulzbot pro to use 4 different materials to print an object. If not what would be the best choice to do so?
If you managed it, your full available build area would be exceptionally small. You would not be capable of IDEX, leveling the other head, or reliably homing it. If those issues were resolved, then you could. But it would be really tough
Modifying the TAZ Pro will be difficult if not impossible. Even if you did so, the reduction in useable X axis would be significant.
Two possibilities come to mind, first a Prusa i3 MK3S+ with an MMU2S upgrade. Second would be a Palette 3 or Palette 3 Pro. There are probably other options as well.
Both of these options use 1.75mm filament. The Prusa solution is a complete separate printer so aside from having to stock 1.75mm filament for your multi-material prints it should solve your needs.
The Palette 3 or 3 Pro uses 1.75mm filament and feeds it to your existing printer (which normally uses 2.85mm filament). Other Lulzbot 2.85mm tool heads have been modified to use 1.75mm filament, so I would guess that a similar modification could be made on the TAZ Pro. Many of the modifications I’ve seen are easily installed / removed so existing one and two material prints can use materials you already have.
Once you figure this out, you could even use a second Palette 3 on the second extruder.
My recommendation would be to go with a Prusa printer.
Thanks for the input.