Manley Labs Jumbo Shrimp has 200ohm output impedance and should drive those 509's to perfection. This is a pre amp that will inject some real organic, rich tonal beauty with plenty of rise and decay, its a very special sound and you can buy them for around $2500 to $3500. Has radio controlled remote too not inferred.( RCA only if that's a big deal ) Also, pre amps are very important to the sound of the overall system, very important to find the one that sounds best for you, it would be good to try a few before making your mind up.
Matt M
Matt M