The BA still has a small amount of hiss IMO but it's very slight and you'd have to be listening for it to really pick it up (without music playing). Not generally audible during music playback. Using the RE262 with 150 ohms impedance with the Studio V 3rd ANV I could detect 0 hiss, even without music playing. So there is some merit to the ohms impedance playing a roll in conjunction with the IEMs sensitivity. I have a feeling the 350 would have 0 hiss as well.
So iems with lower impedance have a louder hiss? Because right now my fiio e03 makes a very audible hiss with my ath-ckm500 (16ohm)