I just got the fostex ebonies and tested them on both. The noise floor was so loud even at moderate levels there was a hum. Right when I plug it into the RME it has the blackest backround, without any added help (ebtech humx, ifi idefender 3.0 with supposedly clean 5v injected from wallwart. I'm wondering if the ifi defender 3.0 would have some utility though, cutting off the power from the usb cord, since the rme doesn't use it. But I'm kinda wondering if i should just let it do it's thing.
Measurements show it doesn't really need it.