I agree with the others here that the GS-1 is a very transparent amp and excellent at enabling you to "see through" to your source. You may have to experiment with different sources to see what works best for you. As far as headphones themselves, I can only speak for my experience with AKG K701s and a couple of Grado models - both sound extremely good with the GS-1. The amp itself is impeccable in terms of build quality. Downsides - well, I like the amp so much that I decided to move up to the GS-X, and eventually when I get it, I may be put into the position of deciding whether to keep the GS-1 or sell it! One final point - I did get the upgrade stepped attenuator on my GS-1 - since I never heard the variable volume control, I can't say whether it makes that much of a difference (I assume it does), however as common with all stepped attenuators, you do lose some fine control over adjusting volume levels - in most cases, I haven't found this to be a problem but in a few instances, having a variable control would have been helpful. You can compensate for this somewhat using the gain selector switch, but the GS-1 only has 2 settings - high and low (thankfully the GS-X has 3).