1. I don't think people buy super hi-end audio systems to listen to Hip-hop, Trance, R&B and Metal. If you're into those genres, I wouldn't recommend you pick up a Stax 009. With Metal, you're not worried about the drum stick sound as it strikes the cymbal, and the way it resonates in the recording environment. You're not worried about the Upright bass timbre in Jazz, and hearing the sound resonate in the wood before exiting through the f-holes. In Metal, the bass is run through a distortion pedal, then an amp, THEN miked. Metal is about the power of the music as a whole, and you don't get caught in the nuances of the music.
I know plenty of people who listen to hip-hop and metal on summit-fi systems. I myself do it.
Anything that is recorded well will sound just fine on the SR-009.
As for stuff that isn't recorded well: personally, I think the whole "highly transparent headphones demand the best recordings" thing is an exaggeration at best and at worst a total myth. In my experience it's headphones with more distinct colorations that sound bad with poor recordings. Granted, a revealing setup will make those flaws in recordings stand out all the more, and in that sense it sounds "bad." But it's the headphones with very distinct U shapes that make bad recordings sound painful. The SR-009 will make recording flaws stand out, but they wont sound offensive. It's obvious but still highly listenable compared to a lot of other headphones.
The whole system needs to be considered. It's all about the sum total based on your tastes. People who call the HD800 and SR-009 thin, bass-light, and "unmusical" for example tend to be those who don't pair them up with the right equipment in my experience. Both are very chameleonic of upstream gear. The SR-009 for instance can sound more thin and analytical on something like a BHSE or KGSS, yet sound much fuller and more lush on an LL or WES.
2. Genres like Trance and Hip-hop are not well produced. Though it's getting better, I, as a fan of trance music, have gotten further away from it as I get into higher end audio, because it's usually produced horribly. Independent producers are different, but I'm talking DJ mixes. Even DJ's with Money, like Armin Van Buuren, produce mixes that are usually bright and not well done. Not to mention, it's a compilation of many producer's music, all mastered in a different way, then mastered all over again to be consistent within the mix. I get way more satisfaction out of trance by not listening to it on a quality system. For trance, I often go "mid-fi" to get the most satisfaction.
A generalization regarding production values.
But even granting that on the whole these genres have less in the way of good quality recordings, I still find a proper high end setup renders them perfectly listenable (unless it's really awful. In which case they will sound just as bad on mid-fi stuff if not worse).
3. The very best headphones in the world, are they terrific all-rounders? Or are they pretty good at most things, and excellent at a few things. Like 009. It will do anything. But acoustic, Jazz, Classical, instrumental, and vocal sound best. If you're a dubstep freak, you just don't dive into an 009.
I'd rather have an HD800 and the right amp (ECBA, ZDSE, Stratus, etc.) for listening to electronica than any mid-fi headphone. Similarly the SR-009 paired with the LL sounds gorgeous with most electronica.
To go back to the FI-BA-SS which prompted your questions, I think the same thing applies: it sounds fine with electronica. By no means is it a "classical only" headphone.
Really, I find most of the music recommendations passed around by audiophiles to be terrible. Since we're on a role with generalizations here, it seems like so many audiophiles have terrible taste in music. Honestly, as soon as my gear starts dictating the music I listen to, it's time to quit. That's a very bad sign.
