petaluman - I can't be of much practical help other than referring you to Rob Gillum at Coherent Source Service. If the 03a schematic exists, he would have it. There is an aftermarket op-amp EQ called the 'golden flute' in a brass tube. Here's a little context.
The 01 series had a 30Hz EQ for which I don't remember the topology, but I doubt we used op amps. The 03 was 'improved' and also different in that it was a combination ported box with optional EQ. The 03a was sealed and its 'improved further' EQ came with the package. I do know that the CS3 is discrete with all film caps, etc. but may have caps in the signal path. (I have a unit, but no schematic.) The CS3.5 EQ is all discrete, all polystyrene caps (except for the unregulated power supply), metal film resistors and direct coupled - no caps in the signal path. That unit is presently being upgraded. Now upgrades for all obsolete transistors are available and soon there be will a significant upgrade. Still working on it.
So, in general, the EQ keeps getting better, but the only schematics I have are the original 3.5 and 3.5 Renaissance in process.
As I've mentioned, the woofer / enclosure parameters are conceptually similar for the 03a, CS3 and 3.5, but not for the 03 due to its ported bass. Let us know what RG says.
For the record, JAFANT provides this forum for which I am grateful for this way to share insider information among us.