The Audio Technica AD and A series have a reputation of being easy to drive. Both of these series have really great soundstage. But I did notice from your post the model number looks to have changed with the X added at the end. Is this a new model of the 900 series. What are their specs?
I prefer solid state headphone amps for inefficient headphones and low impedance headphones. OTL amps with high impedance headphones kick some but too.
For a headphone, desktop setup I also like the looks of glowing vacuum tubes.
