It all depends on the sensitivity of your IEMs... I hear no hiss out of my R6 Pro 4.4mm jack with my Kanas Pro, some hiss with my DM6, and more hiss with my S8F... I have an iEMatch that I use when it bothers me, but most of the time I can ignore it, except during quiet segments of a track...I experienced significant hiss sounds with both Sennheiser IE8i (16 Ohm) and Noble Audio Encore Universal (~30 Ohm) when using 4.4mm balanced cables. In early April, I messaged Hiby customer service about this problem. I was informed that they made some progress on their own 4.4mm impedance adapter and its ETA is "next month" (May 2019). So as of now I'm using only the 3.5mm stereo connector. I will update here if I hear anything back.
If you're using IEMs with 4.4mm balanced cables and don't have the hiss sound problem, would you please share your model?