Beelzebassie wroteHmmm... My Pi B+ only uses about 4% of its capacity (USB) while playing 16_44.1 files, and 10% @ 24_96 (over I2S, when using USB it goes up to 45%).
That's interesting. My problem is presumably elsewhere then. Do you know if using a higher quality SD card might help? Logically I can't really see why as my music is stored on a usb drive but my SD card is a cheap generic one and I can't really identify any other weakness.
I currently have my DAC and my USB HD attached to the same powered USB hub as my wifi dongle only works when plugged directly into the Pi. Could this be a problem?