Note: The original issues I was having with this plugin have been solved, so I'm editing out that bit from this first message and you can just consider the rest of this thread to be tips on how to adjust it to work within BBox:

I found this really nice, FREE guitar VST plugin, that I thought might interest people. If you would like to have a look at it, then it's found at http://www.spicyguitar.com/

It work's ok in WinBB
If I had a piano roll on MacBB I could see what's happening.
If you have Reaper you could save as xml to Reaper and you will have the chord track then you could use https://forum.cockos.com/showthread.php?t=192481 or https://reaperblog.net/2016/04/instant-arpeggios-chords/ on any guitar vst to create strumming, chords and arpeggios. You could import the track back into BB.

I don't have Reaper (I think my OS is too old for it), but I have tried simply exporting any given BBox .sty that included a guitar track, load that into Cubase and run Spicy in there -> No problems whatsoever.
So it's not that the notes aren't there, if that's what you were going for. BBox just doesn't seem to muster whatever it is that is required by this VST to produce the sound of all of them (when in a chord/strum) at once

I also tried different tracks than the designated Guitar track in BBox, but that doesn't seem to make any difference. I have, however, not yet messed around with the "separate strings/channel" item in Prefs, which I only just thought of now....I s'pose I could just try to adopt that workflow I mentioned above and make do with using this plugin in Cubase in conjunction with midi extracted from BBox, but that's a bit of a cumbersome "changing planes" thing I tend to dislike.

I have finish the other job I was doing so I will go back to MacBB and try again.

Always can rely on you to respond to the challenge, eh

I forced it to CH1, moved the keyswitches in mapping down to octave 0, it seems to work now. If you were missing notes it maybe the midi guitar track is outputting on 6 channels 11-16.

That's at least two variables I hadn't considered, forcing channel and the octave thing (which I really should've thought of), so thanks a lot for chipping in. I will be giving these a try and see how it goes. Have another project to attend to right now but soon.

Oh and don't worry, I will let you know either way (I can't stand the hit'n-runners myself)

Right, here's the result: IT WORKS!

In addition to moving the Midi Mapping keyswitches as you suggested (never occurred to me it was defaulted that high), I also had to raise the octave for the track within BBox Midi Setup to +1, and that was the clincher

This is a brilliant sounding plugin, especially for freeware, so I'm very happy you cracked this one for me (and anyone else around here wishing to try this VST). Thank you so much!

p.s. It turned out I hadn't set the prefs to channel-per-string, just as I thought, but it didn't hurt to check. Given that it needed to be set to channel 1 to work, it would undoubtedly not have worked with the 6 channels setup anyway.