I'm using PulseAudio in Natty, with no sound disortion. I can play 5.1 and other audio stream without any problems.
But in fact, both (SB X-Fi 5.1 USB (SB1090) / SB X-Fi 5.1 USB Pro (SB1095) are recognized as full speed 1.1 device instead of high speed (usb 2.0). This leads to some limitations - I can't play audio stream with 5.1ch 24bit/96000Hz, but only 5.1ch 16/44000.
usb 2-1.3: new full speed USB device using ehci_hcd and address 15
cannot submit datapipe for urb 0, error -28: not enough bandwidth