I received my 'Siberia' pads today and have tried them out. The sticky tape I ordered from the link seems to be single sided only so i used a kid's glue stick - very mild stuff that just rubs off if need be. You don't need a strong glue as the pads are being pushed into the headphones when you wear them - you just need enough so they don't fall off when you're not using them.
The pads fit quite nicely. There's about 1-2 mm to spare around the edge but they look very neat.
Comfort and feel wise I find them to be an improvement. Slightly softer than the Ether 2 synthetic pads but still a little pressure on the area behind my ears. The leather just feels so much nicer than the synthetic stuff.
Soundwise, I feel there is bit of a dip. The base is a little more hard hitting, more visceral like my LCD 2s, but there's also a bit of a veil and they are less linear. Not as silky smooth, less ethereal, than the faux suede Ether 2 pads.
I thought that while I'm at it I'd try some ZMF perforated Lamb Skin Universe pads that came as an extra with my Auteurs. They are a little too big so they kind of bulge out of the Ether 2s and I'm not sure how well they'll stick long term. They offer much the same advantages as the 'siberia' pads in terms of feel and comfort. However, I'm liking the sound of these more than both the siberias and the Ether 2 synthetic pads. There's none of that veil the siberias have. They are very linear and, I think, have a better soundstage than the Ether 2 synthetic pads. The music really seems to come alive with these pads.
I should stress that these are very much first impressions. But for now, the Universe pads have given my Ether 2s a new lease of life and I'm a happy bunny.