Enter the modern hifi world. Try this test.

I also use a very similar DAC/amp dongle but strictly for use on my ipad to headphone connection that I only use when in bed next to my sleeping wife. It did indeed improve the sound pretty remarkably, to the point that I sometimes wonder "why do I even need that expensive "proper" headphone rig?" Then I go listen to that rig and say, "oh yeah, that's why". But that's not really a fair comparison since those are significantly better HP's. I'd try them with the dongle but I really doubt it has enough juice to drive them. They take a ton of power for HP's.

I'd still highly recommend one of these dongles for anyone that doesn't want to commit to buying a bunch of equipment to use with HP's.

Hi,

I believe most of the participants here are well and truly in the modern HiFi world. I'd suggest they are some of the most educated HiFi people on the planet, so you start off on a very condescending note to those who likely know a lot more than you about getting the music they choose to sound right for them. 

That said DACs are an interesting area as regardless of 'measurements ' or manufacturer they sound different synergistically in individual setups of amplification and speakers, IEMs and headphones. The criteria is not how great the DAC but the entire system. 

If you want to establish that very good sound can be had from today's less expensive electronics you will find little dissenting here as many of us use inexpensive streamer/DACs etc. There are excellent class D amps for a few hundred dollars. Its just our preferences are not for those choices as sound to my ears and yours is different but I don't deny your belief in 'modern' inexpensive digital technology. But,  I thank you for reminding us that we have choices.

Are 2 Units required to create a design to be 2 channel/stereo?

@kirkwallace 

"Does the cable have to be 3.5m? Can’t be shorter?"

"@frank009 i mis-read your first measurement; you were talking about the connector diameter being 3.5 millimeters; I mistakenly thought you were saying one needed a connector cable that was specifically 3.5 meters.  So, to answer my question, presumably a 0.5m, 1m or 1.5mm cable would be fine for conducting this test."

Hi kirkwallace, your first clue should be this guy doesn't even understand the metric system, you asked him twice as I quoted above. He's had since 6:56pm on to Friday to respond to you appropriately. Stupid mistake.

Yeah, and @zlone asked "Have you had a chance to directly compare it with another DAC? What did you use?". Nothing in his profile. Gone!

Like your system!

To each their own even when ridiculous.   Happy listening.