Hi,
I can't comment directly on the 150AN but I can definately comment on the AN1x it copies.
The AN1x is the best peice of music equipment I have ever bought. It is so good we bought another one. This is in preference to the Nord (of which we also have two) the JP8000, Virus etc. I absolutely love it and use it for every type of sound.
I had a play with the CS6x for an hour or two in my local shop and thought it was pretty good (I don't own any sample based synths). What I thought it lacked was the raw power of the AN1x virtual analogue.
If you buy a CS6x and don't put the 150AN card in it you should be shot. Buy it! buy it now!
Paul