I have the K450s and have auditioned the M50s extensively. The M50 is a big upgrade, both in size of the headphone and quality across the range. You'll notice a big difference.
Also have the 8320s, enjo
Wow if you think the UE6000 doesn't have enough bass, then you are a bass head! Sony XB500 for you, my friend. <$50 if you can still find them, and let us know what you think of them.