A short summary post (again), between my D7200, D9200 and TH900...
Comparing the D9200 vs D7200 driver-to-driver in the same enclosure, the D9200 driver seems better resolving (in the bass, in the mids and in the treble).
The D7200 driver can create more bass pressure around 50 Hz, but the D9200 goes deeper and flatter.
Less bloom than D7200 and much less bloom than TH900, but the D9200 driver is [one of] the most accurate dynamic driver I have ever heard.
Besides, the D9200 is far more resilient vs pad changes, you can try more pads and all of them will sound good, unlike with the D7200 which is more problematic.
The D7200 is an incredible price/performance headphone. It sounds best with its own modified pads. If old enough, no cup mods are needed (midrange forwardness goes away with time). Recommended for people who want calmer treble than the D9200 has and don't want to invest in D9200 cables. It's one of the most linear dynamic headphones I've seen. You are best off with a 2+ years old good second hand pair.
I modded the TH900 extensively, made it much better, but could not change its sonic character or make it considerably more linear. But it has tremendous bass energy, huge sound stage and it's my movie/games headphone. Sounds more explosive sound than D9200, still quite V or W shaped sound. Sounds best with the modded Stax 009 pads mounted directly on the housing with adhesive tape.
The D9200 also sounds best with the modded Stax 009 pads mounted directly on the housing (no mounting rings). If thin/shallow pads don't work for you, try the same mod on the Stax 007 pads, they have same type, but thicker foam inside. If the stock pads would be softer and had bigger internal diameter, would probably be the perfect pads for the D9200. The modded D9200 goes deeper and more flat than the TH900, its bass peak is more like between 25-30 Hz vs the TH900 bass has most energy around 40-60 Hz.
IMHO the D9200 treble tendency (which is more like a Japanese preference than a flaw) is only accentuated by its cable, and it sounds far better with the D7200 cable (and vice versa). I recommend soft pull solid core (~0.3 mm strands) pure copper cables with the D9200, but YMMV. Solid silver might work with some makes, but stay away from silver plated copper, as it's not the best of the both worlds, but the worst of both worlds IMHO (at least in this case). I don't doubt there are worse copper cables still, but it's much easier to make copper right.
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