I think the Vandresteen 2´s are not very hard to drive, so possibly even a modest amp should be able to make well duty, but IMHO there is always something with powerful amps, like a BMW M3 gives you more, even if you don´t drive fast.
It looks like the TX-4500 is pretty high with distortion figures, maybe that pre-out and a class-d amp.... as impedance does not go that low, I think a lot of class-d amps can do really well here, my 5 cents of tips, and it does not break the bank: Some ncore based amp?
One more thing, those phase correct speakers have something MAGIC about them
I do have a pair of Duntech´s that I will never part with, they are simply too good
Impedance curve below, as measured by John Atkinson of Stereophile