I'm looking for a 5.1 external USB sound card which should work with Linux, and should have a multichannel SPDIF out? 
I've already bought this one. However its recognize as stereo device. http://www.ebay.com/itm/USB-External-Optical-Audio-6-Channel-5-1-Sound-Card-Adapter-Laptop-Computer-PC-/361143614328?hash=item5415d63b78:g:21wAAOSwuMFUg9Ks