@timrvt -- I heard the a20i a few weeks ago. I was so impressed that I decided to order the a50i since my speakers are not particularly high efficiency. While I did not get a chance to listen to X200, my understand from talking to a couple of dealers is that they are sonically more similar than different. The a20i being pure class A will obviously offer the typical virtues of that class. It is going to have better midrange and high frequency response (sweeter), but the X200 will give you better dynamics and slam and can drive pretty much any reasonably efficient speaker. Of course this doesn’t mean the X200 lacks in midrange qualities, but from what I hear the a20 is just a little better but at the expense of dynamics. You can’t go wrong with either.