If you're looking for slam and dynamics without sacrificing transparency, I suspect you won't be disappointed with the Hegel on your Magicos. I'm extremely happy with mine in these areas with my Raidhos. I'm using one in stereo mode, which provides 675 watts into 4 ohms. Hegel doesn't specify the output into 4 ohms with the monos, but I'd guess it's considerably more powerful than the stereo unit (contact Hegel and ask them). Of the stereo unit, Pacula at 6 moons says: "I don’t believe there are loudspeakers beyond the Hegel’s power capacity starting with the Franco Serblin Ktêma through the German Physiks HRS 120 Carbon to the Ascendo System ZF3 S.E. and Avalons ending with the Sonus Faber Elipsa and Stradivari". And Harley at TAS says, "I also had the feeling that the H30 had virtually unlimited power reserves." My previous amp was more powerful on paper, but the Hegel is more dynamic and adds more control.
A couple reviewers (including TAS) thought the stereo amp sounded better than the monos--I suppose that's up for debate. Schneider at Soundstage thought the depth was lacking a bit, but that was in comparison to the Luxman which excels there--but then again, Harley says, "the palpability of timbres and images toward the back of the soundstage was phenomenal." I guess everything is relative to what you're comparing to, but I haven't noticed any deficits in stage width or depth. On the contrary, I find the soundstage and image specificity seem generous and accurate.
I use a tube preamp, as you're planning to do, which I think is a good idea. Overall, the Hegel is the best amp I've heard in my system, doing a fabulous job balancing clarity and detail with ease and liquidity. I haven't heard the Bryston, so can't comment on the comparison.