The most sensitive headphones I have are the Shure 215 in-ears. They are rated at 20 ohms with a sensitivity of 107 dB. So, they are well off the 1/8 rule with the 5 ohm Explorer, but they still sound terrific. I didn't detect any noticeable hissing or background noise. Actually, I heard more background noise with the DragonFly when compared to the Explorer using the 215's. Granted, they were plugged into two different USB ports, so it wasn't an entirely controlled experiment. But, that's still what I heard.
At $150 each, order them both from Amazon and return the one you don't like.