You can use a Widi jack with either 3.5mm or 5 pin din connecters, a Widi uhost over USB, or a Widi Master over 5 pin din. It’s mostly a personal choice for what ports you want to use (or keep free for other uses).
One minor caveat is that the different ports have some limitations that vary across the types. IIRC this affects midi clock and possibly sysex. Forget the subtle details.
Not sure what a nixie is.
Sounds like you might have the version of the firmware that adds keyboard support … or perhaps there’s something else going on?
You computer’s Bluetooth should be fine to connect to a widi. If you want the lowest latency, the a Widi bud would likely be an improvement, but that’s an edge case for most of us.
They have a software update available for the MC6 MkII that restores the keyboard in the mobile editor, but nothing available for the MC6 Pro that I can find.
I don’t have a pro, but i do use a Widi Bud with my laptop. I have a widi uHost on my board, powered by the usb port on a Cioks DC7, which in turn is connected to the usb port on my MC6 mkii. This powers the MC6, saving me a power port for other pedals. I have a second uHost connected to an iPad. This ‘widi group’ allows me to connect the laptop for editing MC6 presets, and Future Impact patches as well. The iPad is there for softsynths, backing tracks/ sound effects, and parameter adjustment of the FI, a Source Audio C4, and a Poly Beebo.
I have a secondary group with a uHost connected to a midi keyboard controller. This connects to the main group via a Thru6BT. This allows me to play the softsynths in the iPad, and the Future Impact and Beebo. I can also use the MC6 to call up performance patches on the keyboard, allowing me to quickly switch between sounds/control sets for live work.
Haven’t needed a wire between any of these devices in ages! CME’s Widi stuff is great.