The mod brings its capability to a whole other level. If you max out the amp/cable/headphones, it should be SQ king as far as portable hi-fi goes (I haven't heard the 240, but for its price, it should use WM8741 chips).
A friend of mine listened to my set up and said it sounded like there was a living room playing music in his head.
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IMO the only negatives of the rwak120b/s are price of admission, required bigger footprint, reduced battery life, and UI could be better (and unfortunately, it seems that iRiver is done with giving a damn about the ak120, so the firmware might not get any better).