I have my W1000 amped with the G&W ATH-F100 headphone amp. G&W is a chinese brand and this particular amp was supposedly authorised by Audio-Technica to be built for the W1000. All tests were done by the W1000 and its circuit is, also supposedly, based around the ATH-HA2002 and has a MOSFET output, like most AT headamps, I think.. and it is made in Tsinghua University (like the Harvard of the eastern world and is one of the finest universities in the world - look it up!)..
With regards to the sound, I think it does the job it promised to do plus more. I mean, there is only so much you can expect from a budget component, add the fact that it is a chinese amp, but this particular amp did exceed my expectations, by a lot actually. Bass quality is very much improved, but not an increase in impact. The mids I can't tell the difference, but perhaps a little warmer. The highs are where the amp works its magic - the harshness of the W1000 is dramatically reduced, everything sounds so much more relaxed and smooth without losing the impact - whereas before the highs of the W1000 sounded terrible - very sharp and edgy. Overall, the amp is very 'fast' sounding which is great with the high detail of the W1000 and quite warm for a SS. With nothing further to say, I must mention that this amp is worth a try if you can track one down and very cheap for what it does, as far as I'm concerned..
..and yes, probably you should've posted in the amp section.. and to make this post sound friendly.. here is a smiley!
PS. That smiley is genuine..