EverSolo DMP-A8 with Denafrips Pontus 15th, both have i2S

I believe the I2s interface will use the streamer clock when connecting to your dac.  If your dac has a better clock than your streamer you might be able to configure it to use the dac clock.  Otherwise, you are losing performance.  If you use a ddc, the denafrips ddcs at least do not have an I2s input, you will need to connect the streamer to ddc via some other connection.  The clock in the Hermes ddc is better than the clock in the Pontus dac so you should get improvement as @fthompson251 suggests.  Is any of this worth the money and time, only you, your ears, and wallet can answer.  I have a Hermes ddc connected to my Pontus II and it was worth it to me.  I noticed improvements in soundstage, imaging, transients, and bass response.  All good things.

If the clock in the A8 is a femtoclock then it’s not as good as the ddc.  Likely a toss up to the clock in the Pontus.  The ddc clock, at least in the Hermes and above is an OCXO (oven controlled crystal oscillator, which) clock which is much better.  The Iris uses a TCXO (temperature controlled).  The control of the temp of the clock greatly increases performance in terms of reducing jitter.

Comparing ddcs I would listen to the aspects that were mentioned previously, soundstage, imaging, transients, bass response.  Even treble and midrange response can improve with a ddc.  Noise floor is also lower with the ddc.  You really just need to listen critically and decide what you like but certainly pay attention to the things listed above.

@mbolek makes a fair point, a ddc is often used to clean up USB signals.  That is why I have one as I stream using a MacBook Pro.  Given that your streamer has I2s output you may not gain much with the ddc.  You would be getting s much better clock with the ddc but then using a different output from the streamer which would involve conversions to I2s format when outputting from the ddc to the dac.  The clock might be worth the effort though, timing is significant in the digital world.

If they both sound the same to you then it doesn’t really matter but I would stick with I2S.  The USB connection should utilize the DACs clock instead of the A8 so any difference you hear could be attributable to that as well.

Just so I understand further, feeding the Pontus with USB vs i2S, this only affects which device controls the clock (with USB, the Pontus controls the clock, with i2S the A8 controls the clock).

Yes but you may notice one sounds better than the other to you.

And, to further understand, In either way, the Pontus DAC is utilized. Please correct me if I’m wrong.

If you are using a digital output from the A8 the Pontus is doing the digital to analog conversion. So in both case of usb and I2S, as both are digital outputs bypassing the internal dac of the A8, yes the Pontus dac is utilized.

@kairosman i don’t think that is true.  I run I2s from my ddc into my dac and the ddc clocks the signal.  That’s, among other things, what the ddc is for, much better clock than my dac.  Given that scenario, I believe the A8 is clocking the signal.  There is certainly the possibility that which clock is used is configurable within the A8 but I have no experience with that configuration or the A8.