Do these headphones need an amp?

[theforce]

Hi, i am interested in the HD555 but i have one question.Will these headphones sound good when connected directly to my headphone slot on my sound card(M-Audio Revolution 5.1)?
I use my ok-ish Megaworks 550 during daytime but at night i don't want to ****-off the neighbours. I have read many reviews for em but they didn't mention the performance connected on a PC without an amp.
Thanks for you help.

 

[theforce]

Thanks for the replies. I was going for the HD600 but for that i would surely need an amp and they cost a fortune
I think that my sound card shall be sufficient but i shall see what happens.