My 308 Does A Decent Job In Some Respects, But...

[19and41]

The audio it conveys to my VOIP modem is weak.  About a third of the level of my Panasonic wireless DECT phone that is not put through the PBX.  It's one last ring after I pick up the wireless I can tolerate, but the low audio has a tendency to aggravat those I call through it.  Incendentally, My plans to use it to connect each room of the house were curtailed by the heavily damaged construction wiring from 58 years ago and my old knees and back vs. my crawlspace. It handles 1 or 2 units an my computer table.

[5415551212]

The audio it conveys to my VOIP modem is weak.  About a third of the level of my Panasonic wireless DECT phone that is not put through the PBX.  It's one last ring after I pick up the wireless I can tolerate, but the low audio has a tendency to aggravat those I call through it.

Thats unfortunate What make / model of VOIP modem do you have?
Can you measure what the voltage drop is on the line?
I am not familiar with Panisonic but there may be a programing setting in there for the outside line volume.

Incendentally, My plans to use it to connect each room of the house were curtailed by the heavily damaged construction wiring from 58 years ago and my old knees and back vs. my crawlspace.

How is your home wired? Is each jack a 'home run' common in very old homes.
Most homes around here in the 60's and 70's (~58 years old) were pre-wired by electricians in a linear zig-zag fashion, beginning at the demarcation point a single cable was run looped at each phone jack dead ending at the last jack.
Usually with a 3, 4 or even 6 pair cable.
If you post some photos or a diagram of what inside wiring you have we can give you some advise on home wiring the PBX with minimal crawlspace work.
Also FYI electricians consider 'category 3' cable worthless, here the copper recycle places wont even take cable that small, so often old spools of cat 3 sit in the back of electrical shops or surplus stores gathering dust. I found a spool of 1000 feet of 6 pair category 3 at surplus place a many years back and thought I wonder if they sell that? Then I was back a year later and it was still there, they said make an offer! I can't remember what I paid but it was cheap. So keep your eyes open and find a old spool of cable.
 

[countryman]

Low volume might come from a "deaf" carbon transmitter.