The trim pots are the gain controls for each pickup. You can increase the gains to match another bass you have. Compare both instruments at full volume with the knob on each bass, then turn up these gain trimpots on your Alembic with a small blade screwdriver.
Then, check the pan control on your Elan to make sure the volume at each end of the pan is the same. If it isn't, you can correct it with the gain trimpots. Since each pickup has its own gain control, you can set the pickup height to whatever is comfortable for your playing, or to what sounds nice to your ear, then correct any imbalance of gain with the trimpots.
There is no affect on the tone of the bass when you adjust these gain trimpots.
There's also some info, including pictures in the
FAQ.