I am quite a fan of superlux headphones, they are amazing value for the price, i have a pair of HD681 which are great, though open, and 2 pairs of HD660 old version where i upgraded the cushions to velvet ones, and very happy.
I bought the HD660 PRO thinking it would be a nice evolution to the older HD660, but here is how they compare:
+ longer cable
+ comes with the velvet pads
+ better headband / slightly more comfortable
- the sounds is BAD, the bass is so wrong and kick drums come out extremely loud and compressed
- they are WAY less isolated, more like semi-open than closed, so they don't cut as much surrounding (eg. at work it's not great)