USB-S/PDIF Converter or USB DAC?


I've decided it's time to use a music server with my main system. I currently use one (iBook) with my headphone system with the Grace m902 headphone amp with built-in USB DAC. I intend to get a new Intel iBook when they are released (March/April).

I currently have an unused Wavelength Audio S/PDIF DAC that I could use with a USB-S/PDIF converter (such as Empirical or Red Wine Audio) or get a USB DAC (WA Brick, Stello, ???). Is a dedicated USB DAC preferred over the hack USB-S/PDIF converter route?
budrew
Gordon Rankin at Wavelength claims that his DACs are not isochronous, he says they are bidirectional with error corrrection.

Even those that are, if they properly re-clock the data, should be about as jitter free as you can get.

Steve, heard anymore about the Belkin? Seems to have dropped off the radar.
Belkin stated that the release of the wireless USB hub will be in Sept. The chip maker backed out of the deal.
I did A/B comparisons for a long time with my WA Brick and Gordon is right. Going longer than one 5 m USB cable degrades the sound. I could hear a clear difference when trying three and even two USB cables.