barrygb54 - regarding your equalizer question -
The Thiel equalizer boosts bass to match the natural roll-off particulars of its model (01, a, b, 03, a, CS3, CS3.5.) It is a single-purpose black box with no signal monitoring or upper frequency shaping. Its front panel should show: ’THIEL electronic bass equalizer plus a green LED. Back panel shows: ’Model CS3 Equalizer with 4 RCA jacks. No controls. Is it possible you don’t have a Thiel CS3 EQ?
There is another problem in that the schematics were lost when Thiel was sold to ’New Thiel’. I am reconstructing and upgrading the EQ, but (at least for the foreseeable future) will be addressing only the CS3.5. Note that a CS3.5 EQ works perfectly well for CS3s. the models share the same bass end. There are about 2000 CS3 and 5000 CS3.5 EQs out in the wild.
The 3.5 is a more sophisticated circuit including direct coupling (no caps in the signal path), dual (double mono) humbucking input transformers, as well as selectable bass extension. It became clear that the 20Hz bass of the CS3 could excite room modes, so Jim added a 20Hz - 40Hz option to minimize such problems.
I recommend finding a CS3.5 EQ, which will be upgradable to Studio or Audiophile performance options as well as fully serviceable in its basic form with updated (higher performance) semiconductors that are presently unavailable.