I am struggling to discern any improvement in the SQ of my headphones HD598 and K702.  They are amped by the just out of the box E7 & E9 respectively.  Any o, improvement I will say improvement is only to boost the bass performance by a fraction (E7 on +1) and volume  (E7 by 10%) by circa 20%.   I prefer the K702 & HD598 sound signature unamped (ie without the E7). Clarity is marginally compromised with a hint of hiss and color on E7 especially, but which has graciously rolled off highs. E9 provides a lot more power. Both enrich the bass for...