As you will have noticed, the
subject of a USB souncard for softrocks is a topic of interest on this group.
You have received some very useful input, and there is more useful information
in the archives. One more thought:
look at the sound card recommendations made by Larry Phipps. Larry makes the LP
Pan panadapter for the Elecraft K3. He has a lot of experience with souncards
for SDR. From this link, http://www.telepostinc.com/ use the
LP-Pan link. Scroll down the page to the link for "Sound Card Info." You'll find
info on performance of soundcards Larry recommends for use in the real world of
SDR. USB, Firewire and PCI cards are discussed.
73, KG4LCF, Larry