I disagree at the price point around $150. Ultrasone (580 I assume you mean) can not touch the Pro700 MK2 in terms of bass quantity. I feel like the OP is somewhat like me, willing to sacrifice a little bit of clarity for that huge bass. I find the build quality to be superb, just like the M50. The build quality problem was with the original Pro700, but has been fixed in the MK2. You can't find much more bass at that price point, it even beats out the Denon D1100 in terms of quantity. It has been referred to as an XB500 with better overall SQ. The one and only issue is the stock pads, which can be switched out with M50 pads and then they're perfect for comfort.
Unless you were referring to the Ultrasone Pro 900. Now that is some high quality/quantity bass.