FWIW, Planar speakers have virtually nil radiation to the left and right of the panel, in a plane with the panel. So, you can probably get away with mounting your tt and preamp near the speaker, if you can place them in the plane of the speaker panel. (Hope this is clear to you; if not, I can try again.)
Allnic H3000 is an interesting beast. I do not know for sure that it treats the cartridge output in true balanced differential mode (presence of RCA inputs does not rule this out). As you or someone else said, it does have XLR outputs and the literature does speak of balanced output circuitry, but could be done via an output transformer. I own an Atma-sphere MP1, but I must say I would not consider trying to use 24 ft of phono cable, even if Ralph does bless it.