Late to the thread but you are showing your naivete'- big time. But I know how it is, believing you can make broad sweeping assumptions that must be facts because measurements say it is so and that you are unable to hear any differences in your budget gear.
First off DACs (and CD players) can sound markedly different from one another and not for the reasons you might think. The great sounding units tend to have highly developed analog amplification sections and power supplies that can make the sound more refined, energetic and dynamic. Look under the hood.
Actually don't- just stick to your DragonFly USB though, that's all you need right?
Incorrect, you have to stay awake and pay attention, so here goes. The combination of distortion and noise for the Dragonfly is 76 db. That will be audible. The Dragonfly appears to be a bad DAC, it costs $300. This is Amir's review:
This is a review and detailed measurements of the AudioQuest Dragonfly Cobalt portable DAC and headphone amplifier ("dongle"). It is on kind loan from a member and costs US $300. The Dragonfly Cobalt dates way back to when these dongles came in the form of USB flash Thumb drives: This makes...
www.audiosciencereview.com
The Topping E30 DAC costs $150, has much better performance. Its combination of distortion and noise is 112 db below the signal. This is very close to the limit of what is audible and for most people [99.9%] its performance will not contribute any audible noise or distortion:
This is a review and detailed measurements of the new Topping E30 USB DAC. It was kindly sent to me by the company for testing. Unfortunately I did not get pricing information. As soon as I get it, I will post it. EDIT: just heard back. US cost is just $129.99! This is a bit of a new look...
www.audiosciencereview.com
If there was a DBT between the Topping E30 and anything else with better measurements, it would be nearly impossible to find anyone who could reliably identify which was which as the level of noise and distortion is so low, only the very freshest ears [no one over 30, by way of example] auditing with the lowest background noise have a shot of hearing a difference. On the other hand, the Totaldac-d1-six goes for a little less than $14,000, performs only slightly better than the Dragonfly and much, much worse than the Topping E30.
This is a review of the Totaldac d1-six DAC and headphone amplifier. It was kindly shipped from europe to me for testing by a member at a high shipping cost of over 200 euros. The d1-six costs 13,500 euros including VAT in Europe and $12,400 for export. The latter translates into US $13,816...
www.audiosciencereview.com
So there is a difference, but that difference is not correlated to cost. One does not need to look "under the hood" but it does help to look at the measurements at the outputs.