I'm suspicious of using DLNA for "high fidelity" usage. Look how much effort people go to, to purchase products that use specific types of digital connections. Most seem to agree that AES/EBU is the most pure digital connection with the best clocking and the lowest jitter. They pick this over optical digital and over coaxial digital. All three of these are dedicated wired connections that send nothing but digital audio. Yet the hardcore audiophiles pick one over the other. If there's a difference (and many people say there is), this implies that the timing and the connection method make a difference.
Given that, a network is almost the worst possible transport method. Especially given that ethernet and wifi are CSMA/CD and do retransmission when required. Digital audio needs a constant flow of continuous data. It's not like receiving a file. This is a real time process. Anything delivered via the network is suspect. I would not use a DLNA networked connection for high fidelity audio.
So, if you believe me and my reasoning, you should be using a different method to connect to your receiver, IF high fidelity audio is your goal. What's the best way? A direct digital connection *if* you trust the DACs in your receiver. If you don't, then an external DAC, connected between your PC and your receiver is the way to go. PC to DAC with USB, coaxial digital, or AES/EBU (unlikely), and then DAC to receiver with RCAs.
I've heard strange things about HDMI connections and high fidelity audio. Again, I think it's related to timing issues and/or jitter. I haven't personally researched this; it's just what I've heard from people at high end audio shops.
Perhaps you can borrow an external DAC from a friend and repeat your experiment? Or perhaps you have a digital out on your PC you can use to repeat the experiment?
Just some things for you to think about.
Brian.