Sounds like a bit of an avoid at all cost headphone. The X1 does seem like a good option from what I read about it. In terms of closed headphones, the Beyerdynamic DT 770 Pro 80 ohm has a whole lot of sub-bass but suffers a bit in the midrange and treble. The Beyerdynamic DT 150 is one of the best mid-tier($200-500) headphones I've ever heard regardless of closed or open, it should have enough bass.
The Mr Speakers Mad Dogs should be great too but it'd require some external amping.
The Pro900 was my first audiophile headphone and a formidable disappointment but I learnt my lesson and sorted my taste.
I far prefer open to closed since I've heard my first open can... That explains my limited knowledge in closed backs