Well here's some info on some of those brought up in the thread:
XB500 vs XB700:
The XB700 has more pronounced highs, just very slightly exaggerated but for many people about suitable amount of presence in the highs. The lower mids aren't as forward sounding as on XB500 which leads them to having somewhat "thinner" sound. The XB500 is more "fullier", smoother but for many maybe too smooth/warm sounding why some EQing should be applied. The mids are generally slightly more forward sounding on XB500 but XB700 while having slightly further back pushed mids have a bit clearer sound (without any EQing taken into account obviously). The problem with XB500 is that the bass is pushed in a 15dB boost all the way from like 15Hz to 300Hz (300Hz can't be called bass anymore, that's already whereabouts the lower mids starts at) and this hurts the clarity of mids, lowering 250Hz on a EQ should help quite a lot already (either that or boosting the whole 500Hz+ range). XB700 has a 15dB boost in bass from like 10Hz - 100Hz and it slowly rolls-off from there, so it doesn't pack nearly as much mid/upper bass as XB500 which gives the bass in XB500 a whole lot more impact/punch. The soundstage on both are very close, the XB700 had slightly bigger stage but XB500 had clearer imaging/positioning (I spent quite a lot time comparing them while gaming).