So, I managed to get it all working smile
It's a right mess at the moment --

Raspberry Pi --> HDMI --> HDMI stripper --> Toslink optical --> Audio Alchemy digital interface --> SPDIF --> transformer > SpeakerLink -- but it works!

The Pi also sends serial commands through an RS232 adapter.

I hooked it up and managed to get sound out of the M6... I won't say music though. It sounded like it was being playing through a tin can on a string and the left and right channels weren't in phase with one another. I could not figure it out!

Then I stumbled on this post where AudioImages-Rick saves the day again ! Typing EBOFF fixed all the issues. I have a center image now and female voices don't sound as though they've been telegraphed from the 19th century, huzzah!

This begs the question, what other fun settings am I missing? I've figured out bass, balance, volume, mute, etc. but what's all this EBA business? Are there other more interesting DSP commands that I can play ... er ... seriously examine?

Thanks once again chaps, once I'm done with this odyssey, I'll write up a how-to to share smile

Cheers!
JR