[m1nh0h]

I think I narrowed my search to these two headphones. seems to me that the sony mdrxb700s are overrated. which would be better for an all around music listener but listening more to hip hop

 

[PKPnytheta47]

I just recently purchased the HD518 and I'm starting to burn them in, so far my initial impressions are:
 
It has very clear and defined mids and highs (the 598's have more detailed mids and highs though but not by a mile). These phones actually have more bass than the 598 in my opinion. Please note that I listened to the both of them and they were out of the box when i tried both with no amps (my Sennhesier dealer was kind enough to allow me to do that...=D).
 
After trying out the phones without an amp I actually tried the HD518 with a fiio E11 (which I also bought). I must say the amp does make the HP more rich sounding and increases the bass thumpiness which just made my day! I never even bothered to try the 598 with the AMP since I was very happy with how the 518 sounded after pairing it with the portable amp.

 

[RPGWiZaRD]

HD518 are probably more balanced, XB700 is a bit V-shaped with very strong sub-bass but not so much mid-bass like most headphones have, well it doesn't have very exaggerated highs at all but mids could be slightly more forward still. I don't think XB700 are overrated for the price at all but personally I prefer the younger brother XB500 and think it has more of a hip-hop response as the mids are a little more forward but at the same time they are on the border of being "muddy" due to the bass response extending without any roll-off all the way to like 300Hz (when on XB700 it rolls-off at 100Hz) which is whereabouts the lower-mid frequencies start so this leads to a bit "thick" sound unless you adjust it on the EQ a bit.

 

[nonsupremous]

I think the xb700 is one of the best gems under 100 that is out there.  Unless what you're looking for is that big booming bass...then you're in the wrong place.   They are slightly tuned towards bass but no where near what you'd think given the name.  They are a pretty well balanced headphone with very nice crisp forward mids.  Highs aren't harsh in the slightest.  I had not really considered buying them because I didn't want a beats by dre headphone, but thought I'd take a chance after reading Joker's review.  Glad I did!  Easily my favorite can sub 100 and has been my most used used for the past few months by a long shot.  Oh ya, and if you couldn't tell by a pic....they are extremely comfortable!