There are many iterations of an outboard preamp. I assume you are referring to ouboard preamp pedals. In the past these were nothing more than active tone shaping electronics in a box (Bass, Mids, Treble) that were identical to their onboard counterparts. Active electronics allow you to boost and cut frequencies where passive tone controls are cut only. Lately these boxes have become multi-functional and could be classified in as many ways as there are units.
BTW I also have a J Bass with Antiquities and love it! No need for more tone control there IMO !!!
