Had low volume issues with my CICS....switching tip and ring did the trick.
Also....maybe a problem with the BIX 1A. I did a new install once on a MICS, 8X32. We connected all the trunk lines in, and found that lines didn't work. After a bunch of testing, we thought maybe somehow we got a ground start card instead of a loop start card, but that wasn't the case.
We noticed the lines were dead at the I.T. with the handset...that is, dead until we unplugged them from the input bix field to the KSU. If we connected L1 to co line 1, 2, 3, or 4 input, it worked fine....it's when we started connecting multiple lines we had trouble.
L1 - okay
L1 + L2 connected, both lines became noisy
L1 + L2 + L3, all lines shorted out, none would work
L1 + L2 + L3 + L4, all lines shorted out.
Replaced bix 1A on end of AMP cable and all is well.....talk about a tough day of troubleshooting!