Hi, same issue here. Did you manage to find a solution?
I have a rather large pedalboard, and the HX Effects is towards the end of it.
Before the unit, I have about 5-6 pedals. I tried plugging in the ins/outs of each of them, adding until I got to the HX Effects. They were silent up to that point. Then, I plugged in the in/out of the HX, instrument level, straight into my Twin Reverb Tonemaster.
I power everything from a Voodoo Lab Pedal Power 3 Plus, which is powered by a Furman conditioner. I tried having my board powered from the power supply and the HX alone from its original adapter. Hiss is still there.
Any advice? Thank you