Hi everyone,
This is my first post on the TH-900 thread (as far as I can remember). I've owned these for about for a while now, but I don't know why I've never subscribed to this thread.
I noticed a common theme on this thread about the treble being a bit sharp for some people. I found them to be a bit sharp as well when I first got them. My cheap & non-permanent solution was to use some tuning foam for the Sennheiser HD650 that I found on Amazon (and ebay as well).
http://www.amazon.com/Inside-Tuning-Earpads-Sennheiser-Headphone/dp/B00V35R18K/ref=sr_1_2?ie=UTF8&qid=1432836874&sr=8-2&keywords=headphone+tuning+foam
You have to trim them to shape, and install them under the inside lip of the cups, just like you would a Mr. Speakers doggy treat. I found that they help smooth out the treble significantly. I did a search if someone had already mentioned these, but I didn't find anything about it, so hopefully this isn't a double post.