I still gives a significant boost in high gain. Whoever complains about volume is LOD users with hard to drive headphones. It was meant to be used out of headphone jack though. ZO2.3 is a bit less loud than ZO2.1 that I have though but it still gives a decent boost, for my 64 ohm Q40 I go from 44% windows volume ampless to 19% on ZO2.3 and 14% with ZO2.1 for similar volume levels which I concider quite a significant boost.
Edited by RPGWiZaRD - 12/1/12 at 1:19pm