Hey guys, just got my Grado rs2's and a new Zero Dac/Amp and they look great but when i hook it all up with an optical cable to my PC, the sound just isnt there. I max out sound on my PC and turn the dial all the way up on the Zero and it is still at a very low listening level. Any ideas as...

So I'm looking for a good desktop USB Dac/Amp combo that would work well with a pair of Grado Rs2's. Any suggestions or recommendations out there? Some i have been looking at are IBasso's, a Fubar III, anything else? I'd appreciate any suggestions, thanks!