Do I still need a DDC in between?

@sns  I am not trying to be argumentative but I respectfully disagree with the generalization you have made regarding:

I2S is the native digital pathway in every dac, this is the DEFAULT clock used regardless of input chosen.

"local clock is in FACT a I2S clock", "just a matter of semantics"

That directly conflicts with the statement in the manual: 'When users switch to other digital inputs, the DAC seamlessly transitions back to using the local clock.' When other inputs are selected, there is no such thing as an 'I²S clock' in that timing information is not pipelined separately from the signal data. Please be precise with the terminology. You may want to double-check with Harmony.

Your Gustard U18 mitigates jitter to as low as 38fs according to the specs. Have you seen anything in the other DAC or source that says they beat that? 

@lanx0003 when I went to the last audio show in Florida the DH Labs guys were there. I literally had the Mirage USB in hand to purchase & we started talking cables & equipment. He ended up telling me if I was only going to buy one cable he recommended his Ethernet cable. Saying it would give me the better result over switching my USB cable. 

Unfortunately for him I ended up not buying either cable because I wasn't exactly sure what exact length I needed in Ethernet form. I still haven't committed to buying the best I can afford as I know my current streaming set up will be moving. But I did go to LanShack & get custom length 23awg solid copper conductor Cat8 for now. Individual twisted pair shielding with outer braid shielding as well. An improvement over my basic cable & didn't cost much. Connectors are not as nice as the DH Labs Reunion cable. 

@moonwatcher The 38fs is the jitter rms level in the femto CO (crystal oscillator).  The jitter level at outputs can not be that low.  Here are some measurements taken from coaxial output of various DDCs by Goldensound for their RMS electrical noise and jitter noise at 48khz.

                                  Jitter(rms)   Electrical(rms)   Jitter(peak)  Electrical(peak)

Holo Red                     73ps           2.97mV                213ps           12.9mV

Singxer SU-6              75ps           3.3mV                  225ps            13.7mV

Singxer SU-2 KTE      85ps           3.2mV                247ps            13mV

Gustard U18             453ps           5.2mV                1133ps            22mV

You could see U18 jitter and electrical noise performance is lagging.  That is why I mentioned I could pick up better DDC like SU-6 or micro DDC later on if needed.

@mattw73  Thank you for the recommendation. I like that the cable is affordable, and Cat 6a is more than sufficient for audio applications. I’ll gladly take a $15 cable as long as it works. For the same length, a DH Labs Ethernet cable would cost ten times more (around $300). I’ll definitely give it a try.