Thanks for your reply Solicitous and theducks.
I did have tried different headphones b4 and the results were still unacceptable. I am not a HiFi fan that would expect EZReader to give me super high quality of sound. But at least it should give a decent one.
I think I should try to record a piece of TTS/music clip and upload here for the justification.
Anyway, thanks for the replies. Although they don't really solve my problems, but that gave me all the ways to re-verify the issue. I really appreciate this forum. That's why I visit here almost everyday.
Lance