Macbook vs Squeezebox 3

The converter is where the clocks are, so it is very important.
Be sure to use the Vlink 192, not the Vlink in the black box or the Vlink MkII. The Vlink 192 has better clocks than the previous Vlink versions, and audio advisor has them on for $199. There are much better converters out there, but you'd have to spend at least an additional $250 IMHO.
Steve did not mention; the USB cable from the computer to the Vlink is also very important, as well as the digtial cable from the Vlink to the DAC. Most folks seem to think digital coax sounds better than optical, just FYI.
Why migrate away from the SB3 if it sounds so good? Because it has been obsolete'd by Logitech, i.e. no support?

If you are using a stock usb cable, i can heartily recommend the pangea pc usb cable from audio advisor. It's $35 for a 1.5 meter length and the difference between this and a regular usb is very noticeable, i have the same dac, and i auditioned the pangea against stock usb and the audioquest forest, and the pangea gives a lot more clarity and detail. Which vlink did you buy?

I am actually in the market *right now* for a USB cable upgrade, and this is my short list, in case you're interested:
Kimber USB and USB AG
Audioquest Carbon
DH Labs USB cable
LAT International USB cable
Cardas USB Clear
Wireworld silver starlight
Ridge Street Audio Poiema
...still gathering information, also looking at digital cable upgrade, will add Acoustic Zen Silver Bytes...