I built the very nice Another Filament Dry Box to feed my MMU2S on a Prusa MK3S+. You can view my make. (Note that the make picture was taken while testing, so I did not have all the spool baffles in place yet.)
I do not use a buffer with the MMU2S, instead I simply let the filament back up into the drybox. Initially this caused tangles with mostly full spools, so I designed the baffle. I printed 5 of them and put one between each spool and one on each end. I have then stuffed my desiccant bags into the ends so there is gentle pressure on the two end baffles.
This has ALMOST entirely eliminated problems. A completely full spool can still occasionally jam when the filament is fed back into the box, but once a layer or so is used I've had no more problems.
Sized to fit the drybox and to print on a MK3S+, could be a bit larger on a printer with a larger bed. I've included the Fusion 360 file I used to generate it if anyone wants to remix for a larger bed printer.
The author marked this model as their own original creation.