Duet FireWire Audio Interface (Mac) - Reviews
Pros: Useful for studio recording as analog-to-digital converter and rich sounding as a DAC.
Cons: Uses Firewire, so connectivity may be an issue for some. Can be converted to USB C through use of adapters.
I've had this unit since 2007 and it's been an integral part of my home recording studio environment. It also works brilliantly as a DAC and easily drives my Sennheiser HD800 cans. 
Pros: Great
Cons: None
Owned this dec for 4 years, works beautifully.