Usb or Optical

You may not agree, but your reply indicate you don't understand the reasoning (despite the fact that i laid it out).  USB is asynchronous. It simply reads bits into abuffer and is then reclocekd with a high quality clock. 

You may be theoretically correct for your point of view, but like I said, it all depends on how good the USB-to-i2s receiver section is on the DAC.  In every scenario I have tested, the S/PDIF connection always sounded better than USB.  In some cases, the USB was just horrible (yes, even on a $16,000 DAC!).

for audiomike33, I can definitely see how USB would be the superior outcome here because he is comparing to an optical output from a computer motherboard.  Once you get into the really nice S/PDIF transports, such as the Pink Faun PCI card, things become a lot more difficult.

@audiomike33  - you can continue to use your current USB output if you are happy with it.  Upgrading to a Pink Faun S/PDIF card will improve the result.  Adding an external linear power supply for the Pink Faun will further improve the result (though I doubt if you are going to spend that kind of money).

Im interested in the Pink Faun Card, how money we talking ?. If im going to notice it and its not to much money im game.

Well did some searching and its not cheap and seems like not a common card you could find on ebay used.  So are we talking like ohhhhh yeah i can really hear the difference ?

It depends on the quality of the USB controller. I've seen some devices (Raspberry Pi) where it seems to make a lot of difference. I always go optical or Spidf whenever possible. 

All things considered, USB should be better. It does depend on the interfaces though. Optical has the advantage of minimal electrical noise contamination, but is, in general, much higher in jitter. I have had very good results with an MIT optical cable but for your application USB is the way i would go. As I am learning of late, jitter has a serious impact on sound quality, much more so (i would think), than ‘noise’. I’ve now heard a jitter-free signal delivered to a familiar system and the difference when clearing jitter is to me, quite remarkable. To me it would suggest that the digital reconstruction filters of average DACs / digital interfaces get the job a bit messed up. I am now a believer that clock-timing is so important for best results.

Just to throw a monkey wrench into this. Another option that hasn't been mentioned is a second ethernet port on server, this way you avoid the lousy motherboard issues with usb or optical. Simplifies network as you can do server>FMC>streamer/usb renderer or streamer dac. I use this configuration with Sonore OpticalRendu as streamer/renderer. You can also do server>whatever ethernet devices you like. This also eliminates the need for a network switch and the added cabling necessary with it.

When speaking of optical here, I'm not talking about Toslink.