You will need hex keys and to remove the long bolts from the underside. That will allow you to remove the lid. I used two-part epoxy for a really good bond. You won't regret this upgrade but may I suggest doing it one at a time to ensure you like the result?

Best to feed the clock into the U18 in EXT mode, with I2S feeding the X26 Pro in INT mode. This provides the clock to both units so a single output clock will do fine. The best clock cable by far is the Tubulus Concentus but the Harmonic Technology is pretty good, too. SR Purple fuse is great...

Just to add to the above, I feed a clock to my U18 DDC and that passes through the clock via I2S to my X26 Pro DAC, so they both benefit.

Ah, that was nice of Brett but then he is proper a gentleman. Most of my system uses Big Pads but both the Rendu and DDC/DAC/clock are on Big Pad Plus and they are truly remarkable. I'll be getting my Sig Rendu SE upgraded to Deluxe version later this week. I can't wait to hear the difference.

Bad idea for squarewave clocks. Won't matter for sinewave clocks.

Hey @Jake2 all good here. That's a nice discovery. I found that the Tubulus Concentus cable seems to have even better shielding than the Harmonic Technology. I also take care to dress them carefully so as to not touch or come close to other cables. I did play with some shielding sheets some...

The kicker may be the gradual lack of availability of SR Oranges as they are no longer manufactured.

Thank you, guys! To explain: I use an SR Purple fuse in my DDC/DAC combo and my streamer. That's 6 fuses because in the UK we have a fuse in the cable plug, too. The effect on these digital devices is profound and revelatory - I'm sure I don't need to tell those of you who have used one...

LHY is not the only brand of clock available!

There are two different cable requirements for the possible clock waveforms: 1. Squarewave clock cables require a very precise impedance match 2. Sinewave clock cables require very good shielding This will, in a way, determine preference. My AfterDarks are sinewave and I chose Tubulus...

I have stated several times in this thread that I prefer a sinewave clock. Having seen the LHY square waveform, it looks pretty poor, too.

Yes, I use two sinewave clocks and have a Mini Circuits filter on both outputs. It does further improve sound quality. The 50/75 ohm mismatch is not a thing with sinewaves.

In my opinion, none of the S/PDIF interfaces can hold a candle to the purity of I2S, which takes a further leap forwards if the U18 is fed by an external clock. This clock is carried through I2S and benefits the X26 Pro, too. No other interface does this.

Not at all, no offence taken.

You should do your research. Gustard did their own implementation of the 9038 Pro, overcoming the intermodulation hump and implementing their own digital filters. That's why it sounds so good.