the 3.5mm output is best for IEMs. Full-size hps like the X2 should use 1/4". Try a different cable on X2. It could also be microphonics from the tubes being moved slightly when connecting the hps. This is normal and should go away in 5–10 seconds if the tubes are good quality. Try new tubes if the ringing doesn't go away.
7/24/16 at 10:11am