Cubeast

For that I would assume any commonly available 5 pin din cable will do the trick.

Most of what is being sold as MIDI cables these days have all 5 pins wired unlike say an old cable from Roland which will only have the 3 pins wired. The reason why you might not want to use a cable with all 5 pins wired is because Atari combined MIDI Thru with the MIDI Out socket and that could potentially cause problems with instruments that also use non-standard wiring. Now ideally what you actually want connected to the MIDI Out port of your Atari is a special Y cable or adaptor which gives you both the Out and the Thru which will knock off about 2ms of latency in comparison to monitoring via soft thru via the out port.

Cubase Lite might work but the more serious versions require a monochrome display

Though it may not necessarily be the case I would start with the assumption that the directional wires are in order on the PCB socket.

How is the condition of the Atari's monitor socket?

Your thinking is most likely wrong. I would hope that your Mega STE is using a different TOS version than that which is displayed by the software in your screen shots....but then the guy who's software you are using pointed that out to you already.

As they say "it's better to have something and not need it, than to need it and not have it".

For me it has always been a music machine. My grandfather was a music teacher and introduced me to it.

Yes that's right, there are a whole lot of important distinctions between HD and DD and I am inclined to agree with you that my analogy is inadequate, I mean I am actually discarding certain things just for the sake of simplicity here. I mean there are just so many different factors that effect the longevity and readability of the magnetic recordings that would probably require their own separate analogies, such as the inverse square law for example. I myself have quite a few adapted floppy disks and they seem to have held up alright but I also subscribe to the very same philosophy regarding their use as you have expressed.

When you cover the detection notch of the HD floppy disk to fake the drive into assuming that it's a DD disk the drive uses the weaker DD mode to write to the disk. The disk has of course been designed for the much stronger HD mode. Verbatim's HD disk for example has 670 magnetic particles per inch with a coresivity of 720 oersteds whereas their DD disk has 310 magnetic particles per inch with a coresivity of 620 oersteds. You can I suppose think of that difference in terms of force like lightly scratching your name into clay vs heavily scratching into it and how one would last longer when exposed to the elements than the other....well there is a little more to it than that but you get the idea.