This Lab Brick LPH-204 USB hub can provide more than 500mA (900mA / port) and isolates the noises, as much as it is possible. Works very well in my system.
http://www.labbrick.com/USB-datasheet-Rev1.pdfThe other very useful USB gadget is the Icron USB2-cat5 extender. Does not require OS driver and can be ordered with receiver with one USB connection or with a receiver with integrated USB hub. The receiver end is powered with a small 5V wall wart, but could be used with a small linear power supply too. As much as I know they use impulse transformer in the receiving unit so ground loop and noise could be avoided.
I am using this model at home: USB Ranger 2101:
http://www.icron.com/products/usb_new/usb20_ranger_2101_2104.phpThis way a computer or a storage could be located as far as 100m from the hifi. With their USB2-fibre unit even more (some 9kms)
If you want to maximize your investment in modern high-end playback technology, these gadgets are very useful and do not cost an arm and a leg.