Shandley - A point to consider, instead of beating your head against a wall why not hire a professional and get this set up right?
FreePBX is free to use that does not make it easier to learn than a 100k Cisco Call Manager platform.
To add to the confusion you are using analog phones with a digital system, this adds an entire additional level of complexity.
30 years ago when we were putting channel banks on digital switches to serve analog lines. The levels were set in .5 dbm intervals (and it may not be millivolts it might be a reference to .775 volts at 600 ohms, remember that db is not a unit of reference but a logarithmic expression of energy) and called “prescription” levels. The precise setting of levels is why your land line sounded so good. The cables were measured for loop loss and the levels matched to make sure that impedance mismatches did not occur. Mechanical echo like you are experiencing is a function of impedance mismatches.
Remember the first time you rebuilt an engine and you put the distributor in 180 degrees out? The boom and carb fire was a great educator to not do that again (please excuse this reference if you are one of those men who happens to have a vagina and can’t change his own oil). Every good phone guy has gotten the levels wrong and heard what a really f(***'d up line sounds like. To the unitiated it sounds like it will never work. Like the distributor analogy golden audio is just a screwdriver turn away.
In this case they don’t equip analog cards with level controls (pity as it is the most efficient way to accomplish the task) so you have to set the levels in the configuration.
FXO tune is not performing god like functions, it is merely sending some tones and roughly setting the levels on the lines. Usually it is good enough that it becomes within the range of the ability of the software echo cancellation facility. However it particularly nasty situations you still have to tweak the results.
Since station ports can’t loop audio back the process can’t be automated. You must have really bad cable or particularly crappy phones (or a combination of the above). We already know you are cheap as you would rather endure all this pain than purchase digital phone sets.
So you need to set the levels, sounds simple but I went through all of this for two reasons. 1) I like to hear myself talk 2) Because it illustrates my original point.
I can no more teach you how to finesse the levels on the trunks than a brain surgeon could talk me through a patching up a blown vessel. It just ain’t gonna happen. You can spend hours farting around with it or you can spend a couple of bucks putting up with an arrogant pr**ck like me and have it taken care.
If this sounds like something you want to do just click the support link above. I won’t be insulted if you ask for anyone other than me.