Who would've thunk it?

Today we configured a Universal Tube Stage (UTS) for placement at the SPDIF output of the Morello computer-to-DAC enabler as discussed here :24/192
All the other bits and mods were left in place and the upgraded output transformer moved after the tube output stage.

The result?
The best square wave we've ever seen from an SPDIF. Even extreme high end CD players output square waves that look like a literal train wreck. The Morello Level 3 is already way ahead on that count but adding the tube output produces an even better looking square wave AND alomost doulble the voltage.

Consider: most digital receivers were written to the AES/EBU spec of 5V but in consumer gear are required to trigger with only 500mv (or less; remember earlier we found the Musialnd to output only 250mv). We've found these devices sound better and acheive signal lock more reliably when given higher voltages to work with.

So a tube output gives a more robust and cleaner output signal from the SPDIF. Which is not surprising considering many tubes have 100-200mhz of bandwidth.

The sound: we could immediately hear more roundness, less edge, with added substance. We will do more listening comparisons and report.
March 1: I attach an image of the Morello DTS (Digital Tube Stage). Clockwise from top left: the 24/192khz USB-SPDIF extreme modded pcb, the DTS output stage, the power transformer (wrapped in MUmetal), the EZ Ultimate Clock power supply, the linear power supply to power the USB-SPDIF pcb (V-USB is cut), the EZ Ultimate Clock module.
Sound is impressive - bigger, smoother, more dynamic, more musical etc etc. We're enjoying this.