"The original was coded on a CPC 6128 in the MAXAM assembler and then ported to the Spectrum using a special cable the Olivers had built for them. True cross platform development and all in their bedroom!"
Interesting that you mention that.
It is more than just a cable, it is a Z80 PIO hooked up to the bus on the speccy side, and the printer port on the amstrad side. I say is, because contrary to popular opinion, it is not lost. It is still sitting in a box in my private collection, where it has been for a long time. If I can find the driver software, I will have to dump it and create a schematic of the hardware.
On a related note, I must find my collection of master and sample tapes and dump them too.
If anyone wants me to, I can take some photos for verification purposes. It will take a few days though, need to get at the box in question. Hell, if ElReg wants to take a look and have a fondle of this one-off piece of hardware, get in touch.