I agree with your impressions. The D9200 is a more balanced take on the TH900's sound - it is basically a continuation of the D7000's legacy, IMO.So I had the chance to try out both the Fostex TH900 Mk II (stock pads and cables) vs. the Denon AH-D9200 (also stock pads and cables). I intentionally kept both at stock configurations because I figure if you're going to be spending over $1000 on headphones, they should be designed well enough without having to mod the hell out of them for a good sound. Thankfully, both sound great with their stock cables and pads. I didn't use a fancy amp/DAC to be honest (Sound BlasterX G6 since I'm more into gaming than music), but again, I found these headphones very easy to work with.
I managed to snag a new Mk II for about $1200, and I got the Denons for about $1600. The two headphones are very comparable, but here's the TLDR version: The Denon 9200's are great - but their price tag vs. the TH900 doesn't justify the purchase.
I tested both headphones for both music (mainly movie soundtracks and 70's/80's/90's/early 00's Rock music) and gaming (RPG's, FPS, RTS's, atmospheric games, etc.)
Some specifics:
Bass - The Denons have very tight and controlled bass, can really handle the lows very well, but I just found the Fostex to be deeper feeling and just more fun. You FEEL more with the Fostex vs. the Denons. Both headphones handle deep bass like champs.
Midrange - Both perform well in the midranges. I think the Denon is bit more technically precise, given that they're closer to reference headphones (as others have stated) than the TH900, but I didn't notice a massive difference (again - it doesn't justify paying $400 more). Neither headphones' bass frequencies bled into the midrange.
Treble - I will admit, without proper EQ, the TH900's treble is exhausting. The Denon's are better out of the box when it comes to those piercing highs. However, with the right EQ, I was able to control the massive V shape of the Fostex's and bring them more in line so that the highs don't assault the ears. For gaming, the V shape is better - for music, not as much depending on what kind of musical experience you're looking for.
However, whilst others have issues with the treble on the TH900, I'm very much a huge fan of it. I can acknowledge that its brighter than most of my other headphones; however, I simply love its implementation of a "V-shaped" sound.
In any case, I'd take the TH900 Mk2 for dance music, and the D9200 for everything else.
Will you be keeping the Denon?