Well, I believe chances to get a fairly priced USB->sound stick to work are reasonable big, as long as it's a simple device.
The commly used hardware for these small devices are C-media chips.
I think asus does maintain a list of compatible audio hardware though.
To use usb hubs, you might need a firmware upgrade (asus or custom).
You definately need it to use audio.
I've seen hardware which failed on old firmware, but works in my configuration.
I have a USB hub, with a 15 euro brandless soundstick, a multi memory reader with 2 type of cards in it (simultaniously), and a printer. (2 printers to be honest, but the other is parallel)
I think audio won't be used by most people that much (but I think it will be if it can be easily used for online telephony/VoIP/SIP)