The D9200 is certainly brighter than the D7200 and the D5200; however, as you've mentioned, it is not unnecessarily bright as to be categorized as sibilant or strident. The entire treble section is crisp and detailed. The lows on the D9200 were also the most linear of the 3, but it was still a little north of neutral. However, the bass texture is fantastic on Denon's flagship; you get good layering, and some fantastic sub-bass, to boot. Basically, the D9200 has one of the best bass presentations on the contemporary headphone market.No idea. It seems their Dx200 series has different types of wood utilized with 5200 and 7200 using wood with 5200 being dark, and 9200 being bamboo. But, I have read that 7200 is warmer sounding with seemingly rolled off a bit up top compared to the brighter 9200. IME D9200 didn't get peaky although can be considered bright, but not Beyer peaky type response, and the best part was very interesting bass. It expresses bass really well. It will cause you to listen to music that was mastered with bass as central focus.
If you want better sound, Ebony over Teak. Who cares about the looks. Paying big money on how headphone looks seems like a big waste. Headphones have no real practical value with it's looks compared to other types of products.
In any case, I would pick the Teak over the TH-X00, but there is little to split between 2. They are both very good headphones in the same price range they inhabit.