I will do some test as I own both as well. With the quick A/B I did, I prefer the sound characteristics of the ZX507. Less noisy, more precise and laidback sound. Somewhat lesser but tighter bass. The iFi Hip Dac has more of an in your face kind of sound, very much alike my iBasso DX160 as well. Both sounds good to me but they have a different flavor. I've been using Aeon Flow RT open on 3.5mm SE on both, I'm waiting for my 4.4mm BAL cable.
The Hip Dac seems to have much more power on tap. On the ZX507, I'm at 110/120 high gain for a properly loud listening level and I seem to achieve the same on bout 2/3 of the Hip Dac low gain.
I will try out later with my iems and 58X since I have 4.4mm BAL for both.