the latency is determined in the DAW or sequencing host, period.

if it is solved by higher buffers, that's that.

Well, as to SINE it can't be a universal issue, I have several instances of it in every project for a while and it looks as snappily as anything does here. They're not gigantic instances of 100 articulations or anything. but in itself it loads fast, off of an external SSD.

What I do is go to an extant Synchron, to Control and right-click directly below the name & copy and paste it to a new instance. if there's nothing instantiated it's quicker to just load one of my user presets and do than change all of it.

sometimes there are variances in the Dimension controller but in general I have consistency.

Also the BBO libs here so far do default to CC1 for veloXF. something like Synch. Strings pro are the old paradigm from VI, CC2.

My preference whenever available is surround-to-stereo, I don't have a surround configuration installed.

I stand corrected! thank you, I never saw that before

(C0 is what Yamaha calls MIDI Note 24, Roland calls it C1 since the outset of MIDI; VSL uses the latter by default)

bottom of the image; and those will begin at left with C0 aka C1, MIDI note 24

Apparently the Matrix Level 1 combined articulations is set to CC1, for some reason.

no problem: 

Particular DAWs also have the limitation; eg., REAPER does not, it does not make the distinction effect to instrument channel. I don't use it but this is a selling point for fans of it.

In Cubase an effect may be approached to effect this by a kind of back door using VST3 sidechain input if the plugin has that. I saw someone trying it in Studio One to no avail with a granular effect which can use note-ons but the version of it was not VST3, for instance, it's identical to Cubase's handling.

I have only the one anecdote, but I did purchase and use a refurbished MacPro a while back, it was not distinguishable from a new computer AFAIC.

the effect instance does not deny MIDI per se, but it is not made to enter note-ons particularly

I have definitely controlled an effect via MIDI CC in the piano roll, same channel is a limitation unless you use channel = All, having dedicated one port to it. should work, unlike the above I have not done

the instrument channel is not built to input audio at all.

you have to instantiate whatever it is as an effect.

this is true per se, on either platform, any version

This has occurred numerous times over years now. I tend to doubt it's particular to this installation, because it's appeared on every installation I've had for a long time. More of a straight report than a request for help tbh.

When there is a switch in the matrix by KS and a KS to a cell in the dimensions at the same time, the cell switch variously fails (not 100%, somewhat consistently but it could get it right some of the time), either to switch at all, or last night switching to the wrong key. Not always the same wrong key, more often than not has been consistent, but close the VI channel and come back it may be a different mistake. EDIT: it is not 'in every case', but it happens frequently enough to be maddening.

Happens on render as well. Placing the switch earlier is not a solution as far as I can determine, and not always viable anyway. 
Latency settings do not appear to be particulary meaningful here either. Right now I do 192 samples which my audio interface assesses as round-trip 8.5ms. But same thing on a much less robust machine with 512 or more, and/or with no audio interface, etc.

This is in VE Pro 7, VI Pro both most recent version. It may be more prevalent in larger projects but I wouldn't be confident to assert that as a fact. Chances seem higher that if there is double switching _and_ a vertical dimension switch by CC that it will fail, but I cant show that statistically without being very methodical, and it doesn't seem it would be too fruitful to embark on that mission either. I was looking at a pretty involved preset it would be a problem to reconstruct say inside a single matrix to work around it, but I isolated it to a specific change I could and did effect.

An instrument library is going to need a license for every distinct instantiation, computer-wise. The names in the elicenser application are quite specific, and in the case of a library with a standard and a full version this too will be apparent.

I think at this point it's only going to change in projects like this with better cores distribution, because in isolation/the standalone it doesn't occur. It's fighting and losing a battle with other things in a VE Pro project with reasonably playable latency. Def significantly more frequent an occurrence here with duplicated channels of one mic each, or the mics selection has no impact really; the overload factor is multiplied.

Well, for me "8th notes" is too imprecise to have much of a thought about. Durations could vary quite a lot for that. If you mostly mean a note which pretty much takes up the entire duration you aren't going to want a super-short or staccatissimo articulation, but detache may have a too-soft or too-slow attack. It's very specific, contextual and there may be more than one answer; and in general I'd advise to expect to pay a lot of attention to articulation and embrace frequent changes.

Well, VSL doesn't run Syncrosoft so they can't really know. Yahama/Steinberg owns it and I wouldn't assume they're going to indefinitely.maintain servers for it after abandoning it.

In your position I would download a trial of current VEP or if possible VEP6 to see if it's simply VEP5 isn't cutting it with the OS version. Then, if not, a trial of a more current Vienna Instruments.

the point that sticks out for me is it working on OSX.9 but not on .11, on top of some older VSL versions.

Perhaps only one, which you may have done already: run maintenance/clean up in the elicenser program.

Polyphonic things like strings may use both. Another immediately apparent sign in the VI interface is the lack of layers, in which case there's no use in it [VeloXF]. OTOH certain of the BBO libraries don't respond to velocity, 1 is same as 127. In these cases I go with modwheel for dynamics/timbral gain, and assign the slot xfade to CC20, if only because it appears in several of my CC lane presets in Cubase as it is.

For instruments designed to use it it is; the difference which is immediately evident is libraries where velocity doesn't do anything, it's all Velo XF. For something monophonic solo, velocity brings timbral change along with volume. Plus, in highly articulated libraries of VSL, there'll be dynamics samples for that kind of workflow.

Oh, stupidly I have left out that this is in VE Pro 7.0.1056, connected variously to those three versions of Cubase Pro 11.

Has been the case in more than one project now.

This is definitely one of the weirder things I've experienced in this. 
For instance in the standalone, not connected to my system on the other side of the room, using the onboard of the MBP with its speakers, there is only normal behavior. Except, weirdly, some of the notes in the bottom octave have a release characteristic of a semitone fall which I had not noticed before. Updating back to 1529 now with fresh library files.