I have done exactly this on a Stache 5 – it was rigid, I bought a set of Manitou Magnums that were boost and now run it with boost Revelations.
There’s no centrelock to 6 bolt adaptor that will let you run one of the kits with a spacer either side as the lockring for the 15mm axle covers the bolt heads, so you can’t space the rotor out 5mm to compensate for the spacer on each side.
That Now 8 kit didn’t exist when I did it – it looks neat but is pricey.
What you need is a single sided boost converter that moves the hub 10mm over to the disc side, but there obviously isn’t one for the Formula hub on the front of the Stache 5. I can’t see any on ebay anymore but MTB Tools used to do one. It’s not on their website anymore though.
What I ended up doing was buying one of these. I’ve used it for 2 years and it’s fine. For maximum bodge-ability I’ve wrapped some black plastic around it and put a jubilee clip over it so it doesn’t fall off. It cost £2.30 and has been flawless. I redished the wheel no problem, there’s no threads hanging out of the drive side and the disc side ones don’t have loads hanging out inside the rim.
https://www.ebay.co.uk/itm/Non-threaded-spacer-washer-15-mm-ID-10-mm-length-Galvanised-Mild-Steel/112514387266?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649