I'm starting to come to the conclusion that all headphones are a bit underwhelming for bass. if you have the X700 with a response curve like that and still want more bass you might as well have subwoofers on your ears. I did not realize i was a bass head until i started listening to EDM...for most tracks it makes up half the song, it's the solid foundation the rest of the song is anchored too. There is so much to be missed down low if the headphones can't reproduced them...I started finding *hidden* bass lines in tracks i did not even know had them...and with the highs...well i started noticing clicks, pops, scratches all the nuances in the upper ranges showed up good or bad. It was a real treat. Yes volume level seems to be a catalyst for epic bass on the Pro 900. I do listen to quite low volumes then average...this may be the reason. Some songs are just incredible with the amount and depth of skull crushing reverberating bass...so it must be track specific also.
That is one of my gripes with people who have climbatize their brain into handling high volume and you actually can hear all the detail of a song coming from the headphones or earbuds when your on transit...It blows my mind...I listen to probably 1/20 that volume and shame myself for ever going higher. Ignorance is bliss untill you can't hear....then it's just a problem.
There's another issue, the louder your music is the more distorted it tends to sound, the quiter the better and this is beacuse when you crank up the volume ur amping up ALL parts of that piece of music, and that creates unbalances... and the issue with the xb700 is that ALL that sub bass is great but everything Above like 200grz is SERIOUSLY rolled off, and for that reason I like my Sub Woofer for listening to Mid Bass heavy music [it can't even go deep enough for Dub Step the poor thing] so xD yea Sub strapped to my head sounds about right [I'm getting a cMoy in a few days which is a sub boost... I've NEVER had a sub boosting Amp b4 so technically I've listened to my xb 700's realitlvey under amped for a while now so I'm excited!]
And volume is a catalyst for bass, it's MORE power to drive a bigger wave which always has more impact because it's PHYSICALLY Bigger, but if u want to hear details then go with lower volumes and clean amps, then you can hear the song as it was orignally masterd [another reason I'm getting dt 880 for that cleaner sound to help me better describe bass]