Yamaha bb605 upgrades

[Basshead784]

Hello all. I’ve got a yamaha bb605 which is supposed to have a bass, treble and parametric mid control on the eq, however, the bass knob doesn’t seem to do anything and the mid knob all the way off, takes all the bass out of the eq. Found a wiring diagram online but mine seems to be different in some ways as there is a black box in my wiring cavity as well. Any ideas on how the eq works on this bass?
 

Also I’m thinking of upgrading the eq with a John East uni pre 5 with an active/ passive toggle. Does that sound like a good pair? I have never tried a john east preamp before. 

[jrixn1]

I remember someone else was recently posting about upgrading their 605. He went for Delano.  Start from here: https://www.basschat.co.uk/topic/302794-the-yamaha-bb-mega-thread/?do=findComment&comment=4393821

 

[Basshead784]

Cheers mate