I use it with optical input and it is fantastic. The sound is quite neutral and can match with any sort of headphones and IEs. Through the USB input, the sound is less dynamic and microdetail is a bit inferior.   The tube get really hot if you turn it on for days, but you can take it away if you don't need it.   Included power cable didn't work at all. I got one with $3 at local store and it works fine.   After a year of use, the volume makes horrible noise as its rotating. Using some grease sorted out the problem.   Not recommended to plug...