Thought I would try a couple more options, just in case..
First, I confirmed that the USB sound card works connected directly to one of the Pi USB ports (using a USB extension cable):usb 1-1.2: new full speed USB device number 13 using dwc_otg
usb 1-1.2: New USB device found, idVendor=0d8c, idProduct=000c
usb 1-1.2: New USB device strings: Mfr=0, Product=1, SerialNumber=0
usb 1-1.2: Product: Generic USB Audio Device
input: Generic USB Audio Device as /devices/platform/bcm2708_usb/usb1/1-1/1-1.2/1-1.2:1.3/input/input14
generic-usb 0003:0D8C:000C.0012: input: USB HID v1.00 Device [Generic USB Audio Device ] on usb-bcm2708_usb-1.2/input3
Second… I tried cutting the pin1 wire (+5V power) from an old USB cable, and using that cable to connect the hub, just in case this was causing the problems.. But, it made no difference…
Back to the drawing board…
Speculation: I wonder if the lack of a decent <ground> connection, or chassis, might be causing problems? All the USB power mains adapters seem to have just two pins (line and neutral), and a dummy (UK) plastic ground pin..