Well, I've been cutting up a hideous leather bag and making mini acoustic panels for the Mikros when I can be bothered to open them. There's still something I find brittle about the upper-mids or lower-treble, but it is a range I'm particularly sensitive to.
So nothing worth telling on that front since I haven't even put them in, but as I cut the ugly bag apart, I found it had this sort of woven paperish material in it that I reckon might be a candidate for a porous material to cover the hole. I've come across this stuff before, but I don't know what it's called. Tears apart very easily. I think the closest thing might be dryer sheets, but we do not use those here so I'm not 100%. The pictures look like it, though, Just thought it might be interesting to others - I'm not doing anything with it as of yet. I hope to poke a wee hole or two into the sticker, put in my little "acoustic panels" and then listen to them like that if it sounds decent. If it doesn't, I'll just take it back to (mostly) stock. Can't be bothered opening up and closing these things to try out all sorts of acoustic treatments. I'll leave that to Lors :).