To DDC or not to DDC. That is the question.

Whether or not a DDC makes an audible improvement is dependent upon the specific source, the specific DAC, the specific DDC itself, the connection type, and other variables. None of these devices are created equal, and no one can predict the outcome with absolute certainty unless it is a specific combination that has been repeated times before with similar results.

Noteworthy here is the Amanero Combo384 USB transceiver card (64 EUR) allegedly used in @maprik’s DAC is also used in my Geshelli Labs J2S desktop DAC (300 USD). This Amanero card performs reasonably well, but uses inexpensive Shenzhen clocks and does not provide galvanic isolation from the source. Using an ASUS PC laptop, the USB performance in my Geshelli DAC was easily eclipsed by inserting a Jhoinrch Ti ISOUSB211 isolator (35 USD), followed by an SMSL PO100 Pro DDC (74 USD) using a coax connection into the DAC. This resulted in a noticeable enhancement in audible performance for a paltry 100 USD or so invested. This revelation prompted me to swap out the Combo384 for the better, directly interchangeable Amanero Combo768 USB card, which uses superior clocks and upgraded FPGA (but still no galvanic isolation), and provides elevated performance for <100 USD invested. 

The takeaway is there are are no sacred cows, no hallowed ground here.  

Understanding the quality of USB implementation In your streamer and DAC, as well as the quality of the clock in the DAC that’s responsible for timing the USB signal is step one. If your DAC clock is not the best quality, DDC with a top notch clock (i.e. OCXO) would make the most sense to convert USB from streamer to AES or Coax to feed the DAC. If you’re simply reclocking USB in to USB out, there may be sound improvements, once again only if the clock in the DDC is better than the one in the DAC and DDC has better USB out isolation than your streamer. 
The cost of implementing a DDC adds up quickly. 
You have to purchase a DDC that would supersede the quality of the clock in your DAC, plus additional USB cable or additional AES cable if you’re going to run USB to AES conversion, a quality power cord for the clock, plus it takes up additional shelf space.

As @soix stated, and as everything in this hobby, you won’t know until you try. But considering the cost involved, you have other options for DACs and streamers, even as a one box solution that would most likely improve on your current set up. 

@johnnotkathi 

Worth watching….
 

https://youtu.be/wiU_15NpUn4?si=gaKwY3JsXG0m15It

I watched.  He is right about many factors.  However, I do not agree with him about his assertion that if you need an external re-clocker, then your DAC is broken by design.

State of the art DACs, such as the Berkeley Audio Design, Alpha Reference DAC Series 3, and the Wadax ultra elite DAC, both benefit from a high-end re-clocker.

Just to add a small note on the Merason DAC1 Mk II USB input, as I’ve looked into this a bit out of personal interest.

It’s my understanding that while it builds on Amanero technology, the implementation isn’t a standard off-the-shelf Amanero module, but a modified design with its own clocking and galvanic isolation.

So some generalizations about typical Amanero-based inputs might not fully apply here.

Just mentioning it for completeness.

From what I’ve read the Merason DAC is built with the USB connection as primary which takes advantage of Asynchronous USB. Its made in Switzerland (think excellent watches and clocks) and at around $6,000 retail they put a lot of attention on the isolated crystal oscillators. The USB input is galvanically isolated, as you’d expect. I think its designed to minimize the effect of the quality of source data. That’s the main reason for my origInal question which I meant to be Merason specific. In theory, I don’t think a DDC is needed, but as we know, audio is not about theory. I could try a DDC but I also get @audphile1. Would a <$2000 DDC beat the Merason’s clocks? Doubtful from what I read about Merason.