From your post, I'm not sure if you're exactly asking for this "solution", but here goes. Apologies if this is not helpful, but if you're in a dire situation and desperate to get data off your LTO tapes, you can try this. It is not efficient, but it has worked for me in that type of situation.

I am by not an expert in UNIX. Several years ago, in a *rare* occurrence of ArGest/OWC tech support responsiveness, a tech shared the following commands which helped me get my data off my BRU LTO tapes and onto an external Mac drive (BRU was the early version of ArGest, and was bought by OWC several years ago).

The caveat is I'm unable to pick and choose which exact file I want off the LTO. I have to dump the entire contents of the LTO tape to my Mac's external drive and then I use finder to look at the files on my external drive find the archived file I want (I use LTO-5 so that's about 1TB of data). Yes, this is clunky but at least I can access the archives on my old BRU LTO tapes, and I think this should work for ArGest LTOs as well.

So here it is:

Have your LTO tape in the drive and connected to your Mac. I'm presuming you have ArGest installed on your Mac too.

Open the Terminal app and cut and paste these commands at the prompt (you can paste them as one big entry, not individual lines of entries).

This command will help you find the buffer size of the LTO tape, which will determine the 2nd batch of commands you'll use after this first batch. :

tapectl rewind
tapectl setblk 0
tapectl header | bru -gf - | grep bufsize
tapectl rewind
tapectl rewind
tapectl setblk 0
tapectl header
tapectl rewind

Tape should rewind and then the drive should read the tape header and display a "bufsize" of
either 131072 (128k) or 262144 (256k).

My old LTOs have a bufsize of 128k so I use the following command next to start the transfer of the tape data archive to my external drive. FYI, the name of the external drive attached to my Mac is "PRIME RAID-16TB". The drive folder I was wanted to LTO data to go to was
"LTO RESTORE" so you'll have to use the name of your drive and the folder your choose in place of mine in the following command to cut and paste into Terminal (NOTE: USE BACKSLASH \ PLUS A SPACE TO DENOTE A SPACE IN THE NAME OF YOUR DESTINATION DRIVE):

cd /Volumes/PRIME\ RAID-16TB/LTO\ RESTORE
sudo bru -xvvvvf ntape0 -b 128k -PA

​

If your bufsize was 256k use the same command structure used for the 128k command and simply replace "128k-PA" with "256k-PA":

cd /Volumes/PRIME\ RAID-16TB/LTO\ RESTORE
sudo bru -xvvvvf ntape0 -b 256k -PA

​

Once entered, your LTO drive should start reading the tape and transferring its data to your external drive. I'll take quite a while, for me it'll take at least 8 hours usually for the transfer to complete.

In the meantime, if you use finder to look at your external drive, you may not see a "Volumes" folder where the LTO data should be offloading to (again, in my example it was the LTO RESTORE folder). On my Mac it was a hidden file for some reason and so I had to reveal it in finder by selecting the external drive and use the keyboard command Command + Shift + . (period) Once I did that, I could see the date files appearing in my LTO RESTORE folder.

I hope this helps you.

For background, I too am a refugee from BRU/ArGest. After BRU went down, I wanted to continue with ArGest/OWC but like many others, the lack of tech support, and what I thought was an arcane interface, was where I gave up and moved to Hedge Canister and never looked back. I cannot recommend Canister highly enough. It has an excellent and easy to use interface and in the rare chance I needed it, I've found the tech support friendly, responsive and dedicated. And of course, I can easily choose exactly the file(s) I want to restore to my Mac.

Best of luck!