Suggestions? The sky is literally the limit.
USB:
- m-audio audiophile
- u24
- microdac
- grace m902
- minidac
m-audio Transit usb -> Toslink:
- Anything (dac1, vda1, a/v receiver, ...)
This is obviously nowhere near a complete list. There might also be some firewire options.
And macs are bit perfect out of the box, so the type of transport (usb, optical, firewire) matters less. One of the USB/firewire options would probably be handy from a "fewer things to haul around" point of view, but that's a metter of personal preference. Mostly it'll depend on your taste and your budget.