I just got the T51i and am very impressed so far. I am usually not a fan of on-ear, and still trying to adjust to the fit, but the sound is pretty remarkable. I actually don't find them bass heavy as many others do (this coming from a Stax user, so not a basshead at all either). They seem fairly even across the spectrum, with a touch of warmth. I paid $200 on Amazon, so it's a nice deal considering retail is $300. Build quality is top notch, a welcome change from some headphones I tried as of late (for example, HiFiMan Edition S, which is $250, feels very cheap by comparison). I'll need at least a few days with them before I decide whether to keep them or not. I am not a big believer in "burn in" but perhaps my impressions will change (for better or even for worse) with more hours on them. I have a JDS O2 amp that I will try with them, even though it's a highly sensitive headphone and no amp is required.