I finally got the ADAT Interface working nicely with Session 8. For completeness and closure, here's what I did. The internal 5v0 power supply had 200mVpp ripple on it, so I added an 820uF polymer electrolytic cap on the PCB header pins. This dropped the 35 kHz spurs observed on the 256x clock output from -35 dBc to -60 dBc, which reduced the timing jitter significantly. Then I reverse-engineered the clock tree by tracing the PCB lines and looking at data sheets of the components. I found the 256x (11.2896 MHz) oscillator L-C tank circuit, but couldn't get it to lock on the external input. So I injection locked it to the external clock by soldering a jumper wire from a buffered input trace over to the L-C tank. Of course, I needed an external clock source so I used my Siglent ARB generator. The best settings are: 11.2896 MHz square wave (for 44.1 kHz sessions) with 3v0pp amplitude and 1v0 positive offset, with 40% duty cycle. For 48 kHz sessions, that clock would be 12.288 Mhz. With the jumper wire in place, the unit won't work using the internal clock as the source, but I don't care because it didn't work well in that state anyway. The ADAT I/F rear panel switch must be in 8-ch position and the external clock must be attached via BNC cable. Another cable is needed from the clock output (not "word clock") to the Session 8 I/O box input (in my case an 882 I/O). Regarding the Session 8 software settings: In the I/O window, the Sync Mode must be set to Internal. In the ADAT Interface config, the clock source is set to SMPTE. In the "Window" pull-down menu, mix mode must be set to External Mix mode. After all that, it works great. I can finally restore my old Session 8 sessions from DAT and transfer them digitally over to Studio One using 8 simultaneous optical tracks, instead of only 2 using S/PDIF. One other item: The Session 8 tracks don't line up directly in the optical output. The mapping of tracks 1~8 is actually 1, 5, 2, 6, 3, 7, 4, 8. This is easy to re-map in my Studio One DAW, which receives the Session 8 ADAT optical output on my Focusrite 18i20. Life is good again.