[Darryl Ramm]

Blue 192 today runs fine with all DigiLink systems and all newer versions of Pro Tools.

Pro Tools 10 and earlier is 32-bit software and an up to ~4GB. Pro Tools 11 and later can use much more. You want a minumum of 16 GB on a modern system.

You should be able to upgrade your system. More CPU, more memory and more disk (put your sessions on the *internal* SDD from max performance).

What is perceptible/annoying latency is totally arguable/very dependent on the performer. You will not make any progress asking here for something that is "not noticeable", we are not working with your artists, have no way of telling what they will perceive and all you'll do is start another latency argument thread. If you want the best blanket guarantee/flexibility you will get a high-end HDX system... but that may not be needed at all, and might be less flexible that say investing in more CPU or modern interfaces etc.

You can test latency issues with talent by injecting 64 or 128 sample latency into your current system. Try it blind, without advertising what you are doing to talent. If you and your talent can live with 64 sample delay and resonable plugin choices (no bad internal latency, no nasty upsampling etc.) then you should be able to operate on native. Maybe with CPU upgrades. You should be able to operate at 64 samples on a very well set up systems. You can also easily freeze/commit all other tracks on modern versions of Pro Tools and save a lot of CPU load.

You likely want to be on 2019.6 (or later soon?) and Mojave. Lots of plugin processing improvements there over 11/12/2018.x Seriously do not waste time on 11/12/2018.x, even if you go with HDX. What *exact* model code/EMC is your Mac Pro? Do you have a Metal compatible GPU? (You can find all you need to know online about upgrading a Cheesegrater to Mojave).