My next upgrade

I would suggest focusing on your front-end source first. If the source isn’t capable of delivering layering and spatial cues, enhancements on the back end won’t help much.

1. Get a decent external streamer. The built-in UPnP streamer in the X26 Pro is, at best, comparable to a $200–$300 streamer.

2. Are you currently using a DDC or external clock? If not, consider using the U18 DDC and an external clock to synchronize the streamer/DDC and DAC.

3. Based on my experience with the newer R26, achieving strong layering and spatial cues with the X26 Pro can be challenging. Upgrading to a more capable DAC may be necessary. I recently upgraded to the Harmony micro DAC and the Topping D90 III Discrete, and I finally achieved the spatial performance I had been craving.

4. Increase the distance between your speakers to about 9 feet to improve soundstage width, but maintain at least 3 feet of space from each side wall. Add a slight toe-in.

5. Pull the speakers further from the front wall to better reveal depth and layering information.

6. Treat critical areas in the room, including (but not limited to) the first reflection points, corners (with possible bass traps), and the front wall—consider using a diffuser there to further enhance imaging.

@baylinor  

10Mhz clocks were never intended to improve jitter performance. They were intended to keep many devices in sync and prevent ‘clock drift’ over time in professional situations ...

https://goldensound.audio/2022/04/14/gustard-x26-pro-measurements-f20-firmware-10mhz-clock/

In OP's situation, the proper way to use an external clock, as suggested above that has been used by several users including @sls883, is to employ an external streamer up front, connect it to a DDC via USB, and then feed the signal to the DAC via I²S. A 10 MHz clock should be provided to both the DDC and the DAC. One could potentially eliminate the DDC if the external streamer or digital transport supports both I²S output and a 10 MHz clock input. Whether a sine wave or square wave works better is another subject.

@baylinor  First of all, we're discussing the OP's situation, and it seems you're suggesting feeding an external clock to the DAC only. I just provided a technical source explaining that using a 10MHz clock alone may not improve performance. The OP doesn't have an external streamer, so a DDC cannot be utilized.

Second, a more contentious topic: if you have a network switch, by no means should you connect it to an external clock. The Gustard C16 or C18 provides only two sine wave and two square wave outputs, limiting its usefulness beyond two devices—though other clock generators might offer more outputs. Still, synchronizing multiple devices is the intended purpose of such a clock.

Now, the more debated issue is whether the DAC itself needs to be clocked. Many people seem to assume that the DAC automatically slaves to the DDC’s clock when connected via I²S, but that’s not necessarily true. What I can say is this: it depends—not all DACs behave the same way. It depends on the DAC’s internal design. Some DACs are designed to slave to the incoming clock signal via I²S, while others use a PLL (Phase-Locked Loop) mechanism to regenerate a cleaner clock from the incoming signal for ASRC (Asynchronous Sample Rate Conversion).

The Harmony (micro) DAC then has a unique design that allows the user to select between using the I²S clock or the DAC's internal clock. This is advantageous if the DAC features a higher-grade internal clock, such as the OCXO used in the Gustard X30 or Denafrips Terminator 15th. In such cases, feeding an external clock for synchronization is considered beneficial. Some user here has already tried this and reported positive results.