SDX Plus can be downloaded from
http://www.nyangau.org/sdxplus/sdxplus.zip.
The included ROMs either are the original ROMs from real Memotech computers, or are derived from them, and these images are readily available on the net already. Copying the included driver code is probably ok as it was derived from code developed by Memotech itself, long since defunct. Caveat Emptor.
The boot floppy image includes parts of CP/M 2.2. CP/M is open source and is downloadable here and other places.
The author of SDX Plus and this documentation is Andy Key
(email andy.z.key@googlemail.com).
{{{ Andy