at first I thought you meant external soundcards like these:
http://www.creative.com/products/pro...4&product=9103
I never heard or icemat before, but i would consider sennheiser. not only is their kick ass 150 series full of features and best audio in any headphones period (read reviews, they all say this thing rocks), but it also includes USB converter. Plantronics make really good DSP USB headphones too.
http://www.sennheisercommunications.com/pr-pc150.html
that's my .02 cents
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Pending..