Harman/Kardon Speakers on M and A Satellite Series

Anyone who has spent time with either the M640 or A660 series, can you comment on the speakers? I currently own a budget Satellite, the L655, and the audio is truly dismal, with and without headphones.
Audio is very important to me in the next laptop I get, and all the professional reviews seem to indicate that the H/K speakers are excellent, some of the best audio quality ever on notebooks.
What about using headphones? How does the Dolby Advanced Audio system sound with headphones? This is a pretty important feature for me, so I am looking for any further impressions.
Thanks

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