And a very short time with the S3X it was. I finished my S3X. All assembly manual checks checked and checked out properly. I still have to do the final fine finish of the base - I save the final base finish for last - but I gave the S3X an initial listen.
It sounded great with the planars I have - Dan Clark Audio Aeon X and Hifiman Edition XX. Sounded great with the Senn 6XX. Sounded hard, cold, flat, and bass-less with the 50 ohm Focal Elex. Interesting.
I got the S3X with the mission of getting a good tubed headphone amplifier that I could use with a wider range of headphone than the Crack (which I have and love). The S3X is not as soft-edged compared with the Crack, even with the Senn 6XX being softer itself and with the Crack tube-rolled to taste for more edge.
Even that initial listen is very promising to deliver on that mission. As a benchmark, I built the S3X completely stock. 4 ohm wired. I have the C4S all built up and ready to install, but I'm going to spend some quality time with the stock, C4S-less S3X before I install the C4S.
Off to finish the base finish and get the S3X into regular service. The only challenge had assembling the S3X was working with the small gauge solid core wire. I had to be careful in stripping it not to cut the wire at the start of the strip. And working with solid core wire both with the S3X and Crack, the wire isn't as flexible as stranded wire, so I had to be more careful about routing and dressing the wire.