The Sundara at 300 USD has become a community gold standard in it's price bracket. But if you're still looking in range of what you paid for the 9600s, then the hifiman 400se for a little over 100 is still a good price. Planar magnetic headphones tend to have a bit more punch in the low end while not bloating too hard into the mids, which is why they shake up the market.

Seems like you have a sound signature preference and the 9600s aren't it. Think about what frequencies you like and find a pair that excels in that area. I hated the 9500s because it seemed like there was just no meat to the music I listened to. Then I went with some planar magnetic headphones and everything just came alive. Hifiman has some good cheap headphones so I'd recommend checking them out.

Also, open back headphones are extremely common in the audiophile world so expect some sound leak. If you don't want that then stick to closed back like your hyper x.