Thank you for your answers,
now i connected the DAC 9 to a ROTEL RB 1090 trough unbalanced RCAs. Power switch on 0, plugged everything, press the power switch, BANG! 380w POP in some poor Quad bookshelfs, to the point where it may have caused some permanent damage to the drivers. Do you think that i may have received a defective unit? Should I RMA it?
Also the ground loop noises are back when connected trough USB, even with the ground wire disabled. I'll have to test it, switching back to the STA 9s, conecting the Rotel by XLR, etc. trough optical it's all good (the toslink small lid/cover got stuck in, then fell off)
By the way, about the review, it doesn't say that it's better than a 3k dedicated amp, it says that he never heard a $300 headphone amp (the price difference between 10 and 10H) that sounded this good.: "HiFiMAN's new HE-1000 flagship has impressive highs and also sounds quite good from the DAC-10H. That probably makes for my favorite combo of all, though I recognize the price discrepancy is fairly extreme. Folks running a $3k headphone would almost certainly own a dedicated high-end headphone amp. Still, it's nice to hear what the NuPrime is capable of."
That's why i asked, because the Lehmann Linear is a 900 euro amp and while i sincerely hope that the 10H is better, i wouldn't want to be a bit dissapointed.