The hissing I expected, tube amps are just noisier.
The thing with the microphonics is that some in the Vali thread have stated that just moving the headphone cable could cause them. I'm gonna get a chance to hear the Vali for myself, so I can check it for myself.
Its good to know it does seem to pair well though.
Maybe some units are more sensitive than others, but mine doesn't get microphonics without direct physical contact with the device. Some people have also complained that they get microphonics just by typing with their keyboard on the same table. Anyway, I'm sure both Magni and Vali will play well with the 598's.