There is none. It was only build in because hifi people like XLR outs.I never understood the notion of using balance with not true balanced design. But what do I know.
According to ASR all that matters is numbers. What constitutes to get those numbers is irrelevant. SMH
I wonder why Amir says it's a balanced headphone amp? Is everything that includes XLR balanced for him?
Apart from that i have the absolute opposite experience from listening with it. I think it favors low to medium high impedance headphone while it doesn't feel happy with high impedance cans. Increasing the gain over 0dB creates massive distortion.
It's time for me to buy a Topping L30, A50S or A90 and see what it's all about.