What did a good 10 MHz clock do for your Gustard R26?

@magon so by now you’ve tried 3 dacs. Gustard R26, your modified Gustard and the PS Audio DSD MkI. Just to summarize…R26 is dark and dull, the PS Audio is too bright, snd the modified Gustard is just right?

This begs the question - have you tuned your headphone and speaker system (s) to the sound of modified Gustard so much that the other two DACs don’t sound right? Both R26 units sounded broken. And I’m most surprised about your assessment of PS Audio DSD. That DAC is anything but bright. So my suggestion based on this DAC shootout you have conducted, is to take a close look at your system, room and the associated equipment as I suspect you have created a synergy for that particular modified DAC and now nothing else can integrate. Is it possible?

@audphile1 I suppose it's possible, but if my system has a characteristic tonal balance, why would it be too dark on one DAC and too bright on another? 

But curiously enough, a lot of my system is modified or custom by the same guy who modified the Gustard x20pro. He did my power conditioning (which is based on parallel capacitance concentrated on my system circuit but also distributed throughout the house), my power cords, interconnects, headphone, and USB cable, and modified my headphone amp. Also speaker cable. My Aurender N100 is stock and I've found that greatly improves any DAC it's feeding compared to my previous mini PC. Obviously I really like the sonic character of Igor's work - very extended on top without being bright, deep musical bass, great dynamics (micro and macro), musical details, etc. 

My speakers are stock - Spendor S3/5, and so is my B&K ST120 amp (from the 70's - great amp - mine is excellent condition and low use). 

As far as what parts of my system affect tonal balance, the headphones are the obvious culprit. I have obtained loans or second hand purchases of several headphones and more will be here soon. I really want to give this a chance before I return the R26. 

What I haven't mentioned is that the modified X20Pro stimulates some kind of resonance in my left ear that has something to do with my tinnitus. Certain pitches sound like they've hit a high-Q resonance. Very odd. I'm going to see an ENT about it. For some reason the modified Gustard stimulates the resonance like crazy, which became more obvious when feeding it from the Aurender, while the modified iFi iDSD doesn't stimulate the resonance at all. And the R26, only a little bit. I want to keep the Aurender as it's so promising, and Igor agreed to trade the X20Pro for future work. So my goal is to match the Aurender with some other DAC that doesn't stimulate the resonance. Oh, the PS Audio doesn't stimulate the resonance.

Thanks for your feedback. I'm sorry I made it so complicated. But I have patience. It's been fun to try a lot of stuff - very educational for my ear. 

@magon interesting. So…couple of things…

I’m also using Aurender, but N200, to feed my PS Audio DSD MkI. I have never experienced any brightness with it. The bass is prodigious. The vocals are velvety smooth. So there’s something there in the associated equipment in your system that doesn’t match. Could be impedance mismatch between B&K amp and PS Audio DSD (not sure if you use preamp). 
As to modified gear - I’ve had bad experience with a modified amp. I loved it in its stock form but it was horrible after mods. It caused tremendous fatigue and I couldn’t listen to my system. That was it for me as far as mods are concerned. Keep in mind that a manufacturer will voice their product to be as neutral as possible. Changing parts, even for better quality ones, doesn’t always result in better sound. In addition, selling a modified component becomes more difficult as the sound signature was altered and the potential buyers understand it. It becomes unpredictable and no one can anticipate what it will sound like. Same applies to cables - the DIYers of the world don’t have the means and the equipment to come up with a cable that would work with wide range of components - they usually tune it to their personal preference using the components available to them at the time. 
I wish you luck in your quest for a better dac and have that tinnitus checked out for sure. 

Everyone likes a good 10 mHz clock.

Contacting tech support to get them adjusted for daylight savings time every 6 months is rather inconvenient.

"When you run the clock cable to the DDC on Ext Ref and then I2S from DDC to DAC, the 10Mhz clock signal is supplied to the DAC via the I2S signal. There is no need to run another clock feed as external reference for the DAC. In this case, the DAC clock should be set to Internal. When used in this fashion with I2S It is redundant to run separate 10 Mhz clocks to both the DDC and the DAC. Saves the cost of an additional clock cable."

I'm not super knowledgeable about some of these connections and need a little help - I'm using a Gustard x26 Pro.  I began by using the USB input.  My first upgrade was to use a cheap Douk Audio DDC with a decent LPS so I could use the I2S input in the DAC.  This was an improvement for me.  My next upgrade was an Afterdark external clock.  This was another improvement.  Now I'm reading the above post and I'm looking at a Gustard U18 DDC.  Looking at the back panel of the U18 there is a BNC connector marked as an input "1OMCLK".  There is also a BNC output marked "WCK".  If I understand the post, I can use my Afterdark clock with the DDC and then simply use an HDMI connection to the DAC and I will get the benefit of using the external clock with the DAC as well.  Is this correct?  Thanks for any help.