The mid/upper bass of the TH900s is prominent, but in a very un-abusive way that I find very satisfying and I get used to very quickly.
Other flagship phones I have owned in the past (Grado PS1000s, JVC DX100s, even Denon D7000s and Beyer T1s sometimes) suffered from
a painful bad car-subwoofer bass, losing control of the bass. I found the bass often unacceptable in these phones.
The TH900s may have a little more obvious bass than strictly neutral or natural, but, especially with a good amp that grips the lower frequencies well,
simply has transparent slam that adds what sounds like an appropriate foundation the to music.
Couple the bass with beautifully organic silky detailed mids and vocals and sweet highs and fine comfort (2nd only to R10 comfort), and the TH900s are a real winner,
a candidate for an only-one-phone if I was ever to go that route.
(And, as a bonus, no expensive after-market cable needed! So it may even be a bargain.)
The Th900 has grown on me very much over time, about 18 months.