I’ve toyed around with my 6 quite a bit, and if I was to do it again with the lessons learned, there’s two paths I’d choose:
Build Back Better Upgrade:
32-bit board. BTT SKR Turbo or BTT Octopus 1.1. Both are good. I currently run the Octopus 1.1
To ease the re-wiring of installing the new board (and gain other benefits), change from the standard tool plate to the Hermit Crab quick change plate. Since the board comes with a nice wiring loom, you don’t have to extend the old toolhead wires to reach the new pins.
New toolhead: 1.75mm. Either a Biqu H2 Revo or something resembling a Voron Aftersherpa. With a few extra parts, you can keep your 2.85mm toolhead in service by adding an Orbiter dual-gear extruder to it. It’s easily swapped on the Hermit Crab toolplate.
You can also consider doing a linear rail swap for the X axis to make the toolplate swap part even more rigid.
Magnetic spring steel PEI build plate. Easy upgrade. Well worth it. I use the FYSETC textured dual-sided one.
Klipper is your choice. This machine won’t ever be fast enough to require it, but it won’t hurt either, since you’ll need to do custom firmware regardless with this build.
Basic upgrade:
Swap the 2.85mm hexagon hot end for 1.75mm V6-style ceramic heater with an orbiter extruder on top. An adapter plate to mount the orbiter is dead simple and a v6-style hot end will slide in place of the hexagon.
BLTouch. Requires custom firmware, but you can get a pre-built version of drunken octopus for the BLTouch if you don’t want to learn to compile marlin or Klipper.
Magnetic spring steel PEI build plate. Easy upgrade. Well worth it. I use the FYSETC textured dual-sided one.
The Galaxy series are probably overkill for most people, but they’re built with good components… but there’s been a couple reports that the 2.85mm galaxy stuff had bad quality control. 1.75mm might be better.
For a dual extruder, the nebula might be able to get to work with some custom firmware, but I doubt lulzbot will ever support it in the Taz 6. The Dual Extruder v2 and v3 were both pretty problematic, and with modern components you could easily build your own dual extruder that far surpasses them.