I think you'll need to give us an idea of your budget before we could make specific recommendations. What will you be connecting to this, BTW?
I believe you will need a DAC with coaxial or optical input, which may depend on what PH you have. From what I saw, some models of the PH have optical only, while others have both. Many DACs have both coax and optical if they have SPDIF at all (or they may have something like BNC that can be adapted to coaxial).
A USB-only DAC probably won't work, because it needs to be configured by a computer to output audio through it. I doubt the PH hour is set up to do this, even if it has USB ports.