I'd say any good quality amp 80-100w/ch or more won't hurt, robust with good current delivery, damping factor, not unusually low, should work well. Does not seem a natural to match with a tube amp but not to say a good one with enough power might not have it's niceties.
I recall teh active ls50s are actually even biamped, which does not appear possible with the passives, FWIW. I would not worry about that though with a proper amp in play. ls50s are a bit on the demanding side though I would say...not just any amp will make them sing.