I´m running a pair of Genelec 8040´s with a Benchmark PRE... Before buying the PRE I auditioned the USB model for a few days. To be honest with you, I´d be lying if I said I could differentiate them in a blind test. Do you have a local Benchmark dealer? If yes, I´m sure they can get you a home audition. Or order from a store that allowes returns like Thomann.
I wanted the analog inputs for old analog-output retro consoles, so I went with the PRE in the end. The Benchmark is a very good pairing with the Genelec - most Genelec dealers agree with that too. Many feel it´s the best pairing for them actually. All in all I´m very happy with the combo. It not only does well recorded music well (Diana Krall, Leonard Cohen, Guns and Roses latest album etc really well), but it´s great for movies and gaming too. What it doesn´t like is overly compressed pop music, but that´s just accuracy for you
PS: If you are using them in a nearfield setup, you might want to enable the highest internal attenuation settings in the Benchmark (very easy to change, just a few jumpers inside - it´s covered in the manual). The Genelecs are very sensitive, so they really like the added attenuation.