I typically switch between my Sennheiser HD800s and my Focal Utopia’s. They are both great headphones. But the Focal are a lot easier to drive. The Sennheiser did not not sound as well balanced and natural until I put about $15K of outstanding electronics with a tremendous tube amp (a 300B Woo headphone amp) behind it.
I definitely recommend the Focal… easy to drive, great resolution and bass… even tonal balance. If you have got the power and natural organic electronics… then the Sennheiser (I would not count on a tap on a preamp… typically you need a dedicated head amp to drive a great headphone like the Sennheiser HD800.
I listen to my sennheiser 800s more now… but Focals before my I bought my tubed Woo amp.. with $2K of 300B tubes.