I recently received a pair of 8351b (for another installation in my house), first time I listened to Genelecs.
1. They're awesome in so many ways... The most striking is how well low bass is integrated with the rest of the spectrum. I've listened to a lot of fancy gear in my life, including stuff way beyond my budgets in fancy hifi shops, and never had this feeling of reality when listening to contrabasses or bass guitar + drums in a heavy metal track. They can also reproduce effortlessly a complex signal, e.g. full orchestra, or angry death metal where the drummer and guitarists run a contest of who can play all their drums / strings at the same time and make the most noise
It feels like you just hear everything, with perfect tonality, and with lots of power in reserve.
2a. There is hissing, even with all sources disconnected. I'd say the threshold of audibility for me is around 40cm from the loudspeaker. I plan to try and measure it later when I have more free time. They're currently setup so that my listening position is ~150 cm from the speakers, way beyond the threshold of audibility for this hiss. So for now I can't tell if this would be a bother in a desktop setup (assuming that the 8331s have the same hissing level). It'll also be difficult to test the 8351Bs at my desktop, because they're too big.
2b. My 2c on this topic, I don't understand why hissing would be intrinsic to active speakers. If it's intrinsic to power amplifiers running at full capacity, then all power amplifiers would have the same issue (even with passive speakers connected to them). If it's intrinsic to active crossovers, then it's an active crossover issue. Which I would also have if I setup a sub + active crossover + AHB2 + Kef LS50 (which was suggested in this thread).
This is quite an interesting topic, but would deserve a dedicated thread
Back on-topic, given all the feedback I received, I didn't pull the trigger on the LS50s, instead I sold the AHB2. With regrets, but rationally I don't have any use for it anymore. I plan to go for the 8331s, just not immediately due to the higher budget. And I'm also giving priority atm to saving money for a pair of W371As to go with the 8351Bs, but that's another topic