I think anyone who enjoys the DT770/DT770 PRO should definitely go out of their way to audition the DT990/DT990 PRO. Overall, I find the DT990 PRO sound similar to the DT770 PRO, with the exception that the DT990 PRO has a significantly larger soundstage. I do agree with Glassman's comment above.
NOTE: the following comments apply only to bona fide hardcore bass enthusiasts, LOL.
On topic, I recall reading an old report which credibly stated that replacing the DT770 PRO velour earpads (EDT770V) with soft PVC earpads (EDT330S) had the net effect of increasing bass output. IMO, this would be an interesting and worthwhile experiment for those who use the DT770 PRO as their primary phone.
Likewise, for recreating a club or "dance-hall" environment, it would be fun to experiment with the judicious use of a sub-harmonic synthesizer. Disadvantages would include the need for extra amplifier power, as well as the possibility of literally destroying the headphone's transducers if over-used. Other signal processors like the Aphex Model 204 and BBE Sonic Maximizer would also be good candidates for experimentation.
TravelLite