Hello Mr Gravesen,
Day 5 of being home alone for 6 weeks, just me the cat and the stereo, all ready my ears are ringing, these speakers do make some noise! 
The plan was to build Your SBA 861 PFCR to see what could be done with low cost drivers, then to use the cabinets again for the Discovery 861 build.
I’m now in two minds about this plan and the SBA 861 PFCR, which by the way sound great in my surroundings, how you described them is spot on but when i listen to them i cant shake the feeling there’s better? If you can get budget drivers to perform this well, to be this exciting, what has been achieved with other drivers?
I’ve driven these speakers with my 25w PP tube amp, my clone Dartzeel 150w amp both do a fine job, wasn't until i played them with my clone Burmester 225w amp that they really stepped out of the shade and sat me down, the bass shakes the floor I’ve not had that happen before. These speakers are wonderful. They play nicely, clean, detailed, There’s no reason to not like them as keepers, but for knowing they are low cost drivers i probably wouldn't be wondering can there be more of everything  from costlier drivers? But i do and i am.
While i made some effort to keep the build price down, features creep in adding to costs, if I’d built with Birch ply, the build would've come in at around $1,200.00 NZD about 600 euro, nice price and very good value for money considering performance. However they came in around $1,800.00 NZD. Still exceptional value for money considering performance and entry to commercial hi-fi is around $2,500.00 NZD. i haven't yet compared them to shop bought . 
The baffle timber is Heart Rimu, the single most costly item in the build. Decision to upholster came after discovering the cost of matching veneer.
Outrigger feet laser cut from 8mm plate, Blast and painted.
Builders tip: built in port. We live in the country with a cat, some form of barrier is necessary to stop the cabinets from becoming a mouse hotel,  welded stainless steel mesh should keep them out.
so which project next? Perhaps the Revelator - 851. 
Thank you for such a wonderful resource. 
Regards
Kari
New Zealand