I would swap out the pre-amp for a model with sweepable mids, such as the John East unit (which by the way really calms what can often be a quite brittle top end on the 3-band 'rays), and allows you to really emphasise the low mids. It won;t be 100% P-Bass by any means but a whole lot closer than you'll get with the current pre-amp I believe. The other option of course is to use your amp to do the same thing, but in my experience, it's often a less satisfactory approach, and you'd need an amp with a similar sweepable EQ to find the tone that's in your head.
Here's the link, for £157 it is a game-changer for a 'ray, seriously
https://www.east-uk.com/index.php/bass/mmsr-4-knob-3-band.html