my $.02
If money isn't a factor - then going with the Accuphase P-6100 is a no brainer. There is NO way it's not head and tails better than the E-460. Accuphase is way too much of a performance company and they would not charge twice as much for a power amp than the integrated is it wasn't a bunch better. I haven't heard either amp but I do know Accuphase's reputation.
There is a big debate over the comparison of the A-65 class A power amp and the P-6100 class AB power amp. Same basic price and two different sounds. With owning some Magicos but not S5s, I would guess the P-6100 would come out on top. It all depends if you focus more on the bass or love the texture voices. That's not to say either amp is bad at either. It's almost the difference between tube or SS. Of course, that's exactly why Accuphase offers both. They feel that both are amazing just different. Get both and switch back and forth. That's what I'm thinking of doing.
Other than the fact that you already have a complete DAG system upstairs for the S5s, I would go with the new Dag integrated downstairs with the Alexia's. :woot: