There is an audible hiss from the Garritan CFX that is at its absolute worst when playing chords at low key velocities. This thread (http://forum.pianoworld.com/ubbthreads.php/topics/2827501/1.html) provides evidence that this occurs because of lossy compression used to limit the download size. I just tried playing with the "Compact" sounds, and the hiss was noticeably reduced, but as one would expect, the overall sound was much worse and more compressed sounding. This seems to add credence to the theory that the hiss is due to a compression/decompression artifact, rather than a problem in the recording process.
It would be great if one of the developers could shed some light on if this is the problem or not, and if the CFX could be repackaged as a larger download to fix it. For now I'm a bit disappointed in this product. I had initially thought the hiss was due to my DAC or amplifier, and had planned on upgrading to the full version of CFX, but unless this hissing issue is resolved I can't justify spending more on this product. It's just too distracting when playing quiet passages.