There's nothing intrinsically wrong with optical, provided your source is low jitter. My main digital source is a Mac Mini, which has relatively high jitter through its optical out (>1000 ps), and at least on my speaker rig the difference is audible over other digital sources I've tried (including the Gungnir's built-in USB). For what it's worth, my experience with the Gungnir is that the sound quality is roughly coaxial > USB > optical with the small subset of gear I've tried.
If I was buying the Gungnir again, I'd leave out the USB option and use the money to get a V-Link 192. The total cost is in the same ballpark, but you get a digital source that's measured to have low jitter and as a bonus uses the XMOS chipset, which is generally more reliable and bulletproof than the CMedia chipset.
If cost is no object, there are other options of course, depending on your needs. You might consider the ART Legato or Audiophileo, but I haven't heard either and can't comment.