Can't wait for your impressions !
Yeah, they are pretty efficient so sound nice from anything but might be a completely different beast after plugging them to something like this
I have read they are night and day after balancing (he-400)
After what I read about pairing he4 with proper amp, Schiit Lyr might be hell combo + some nice source, i guess extra low efficiency of he4 will help to be dead quiet with noise floor and gain of mighty Lyr when there is no music or between silent passages
You might also consider the Audio-GD SA-31. This the amp I used for the small shoot out and the pairing with HE-4 is simply brillant.
This is a warm amp with lots of tonal colors, great to tame the 4s treble a bit and bring out the mids.
I will receive a NFB-27 and try the 4s with it but I anticipate these will be too bright. We'll see!