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

@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.

@audphile1 

While I do recognize that my system might have some kind of "signature" as a whole that is obscuring these components, I've had a very good experience with Igor's mods. I started with just his power conditioning (but all stock components at the time). It made my system more extended on top and more musical by quite a lot. In particular it made things more extended by not brighter. Everything he's done since has built on that. I've carried some of his modified components to other people's systems and they bring similar qualities. Like, a long time ago when I still used CD I brought his modified PS Audio Lambda II to a friend's system and it improved the extension without making the system brighter. I've been in contact with folks in the New Jersey Audiophile Society who use his cables rather than the $5000 cables they could easily afford. He mainly takes moderate priced equipment and brings out the potential - so for instance my headphone amp is a Chinese 12AU7/FET zero-feedback design that comes with a SMPS ($100 new!). He replaced all the parts, added shielding through ERS fabric, added damping, and designed a LPS. Many people in the headphone community praise the concept of 12AY7/FET designs, so it's not surprising how good it is.

With the PS Audio DAC, I'm feeding that by a stock Aurender through Igor's USB cable. Tell you what, I'll replace that with a stock USB cable and test it. Then everything will be stock components except the headphone amp. I'll try it with several headphones through their stock cables. Let's see if it changes the tonal balance or component signature.

@magon actually not a bad idea! I always go back to stock cables to set a baseline for a component’s sound when evaluating it. Aurender includes a very nice usb cable if you still have it, worth a try. Or just use any basic usb and power cord. 
Awaiting your updates.