After hours of fun searching for answers... I had to document this for others who have a firebox.
Hardware: Dell Optiplex GX620 Pentium D Dual Core, 4 megs of Mem. PCI Firewire card. Presonus Firebox
( Older PC )
OS: LInux Mint 19.1 "Key to making this all work is ( Low Latency Kernel )"
( Free OS )
DAW Software: Ardour 5
( Free Daw )
1. Load Mint
2. Load Ardour 5 App
3. Load Jackd1-firewire App
4. Now - Install the Linux low latency Kernel "sudo apt install linux-lowlatency" then Configure real time access Add your current user to the audio group: "sudo adduser username audio" And then give the audio group real time access: Add this 2 lines to the file: /etc/security/limits.d/audio.conf (You may have to create it) @audio - rtprio 99 @audio - memlock unlimited (You may have to restart your System here.)
see this link for help.
Now my PC and Firebox are running with no latency