Oppo 105 DAC vs. Bluesound Vault DAC

Many people will say that different dacs sound noticeably different, and some sound dramatically different.  In my experience, comparing half a dozen dacs from $200 to $2000, this has not been the case.  In your case, the Bluesound uses a Cirrus Logic dac chip, and the Oppo an ESS chip - among the dacs I compared were units that had dacs from both Cirrus Logic and ESS, and...I couldn't tell them apart.   Which isn't to dispute what others hear with their own systems...they hear what they hear, I hear what I hear.  All I'm saying is...don't be surprised if you don't hear any difference either. 

In this case "perception is reality" 

That is, your ears are the final judge of what, if anything is better, so if you can't hear a difference, rejoice! :) Use whatever connections you like the most. 

However, I would encourage you to listen to music in your system and then listen to other systems to see if you are missing anything.  Sound stage, do instruments sound real or replayed? Can you tell you are litstening to a stereo? Does the music attack naturally, does it decay naturally.  Do instruments sound real or "hyper" realistic? Listen to buskers on the way to work or school. Pay attention to how the instrument notes hit your ears.  

Best,

Erik