Which box are you talking about? The NAS? At the moment, I use it as a backup device only. I'd prefer to use it as the main music source, but this is "optional".
If I use my MacBook as data source, it offers
1.0 x IEEE 1394 (FireWire) - SPDIF input/line-in - RJ-45,
1.0 x Audio - SPDIF output/headphones - Mini-phone 3.5 mm / TOSLINK,
2.0 x Network - Ethernet 10Base-T/100Base-TX/1000Base-T - Mini-phone 3.5 mm / TOSLINK,
1.0 x Hi-Speed USB - Apple mini-DVI,
1.0 x Audio - 4 pin USB Type A,
1.0 x Display / video - 6 pin FireWire
I have looked around for a USB DAC; they range from 50,- to 5000,- and more. Phew... 8-/ I have no idea whether you can really *hear* the difference between a 200,- and a 2000,- DAC or just pay for it.