I don't own a th900 but thought i could pitch in on the bassy song department?
https://m.youtube.com/watch?v=_J5DXYrYP80
The song isnt my taste personally, but i haven't heard more undistorted bass than there is in this.
This was good
.
Lot of 30-50 Hz boom. With my modded TH900 the bass power is immense, almost as physical as through my speakers.
Out of curiosity I made a sweep test using this track, and compared it with my 007 Mk1 as well.
https://www.youtube.com/watch?v=ukQ6OSs3dWo
The first sample I have heard with both the 007 and the TH900 was 10 Hz (likely because the harmonics). It was much more feeble with the 007 though.
15 and 20 Hz is clearly strong and already at full play with the TH900, while the 007 is still feeble (but already has smoother and more textured tonality).
30 Hz is strong with both, the 007 again sound more pleasant, the TH900 is brutally physical.
40-60 Hz: the 007 has a slight boom, the (modded) TH900 seems more linear but also has some boom.
There is less difference with speakers, since the bones participate more in the transmission of sound with speakers (therefore sub-30 Hz is perceived stronger with speakers).
The rest is linear with both.
This track might be at its best with the Abyss or one of the Audeze headphones, or the HE6, but it looks like the (modded) TH900 has extraordinary (extended and rather linear) bass response for a headphone. With music, the 007 bass is more resolving, smoother and is more realistic with instruments, but the TH900 is still the power king with bass-heavy material. Quite an experience.