From the thread I'm assuming you're talking about a Sterling By Music Man Ray4. If you really wanted a 3 band pre-amp I wouldn't go with upgrading yours, I'd say sell it and get a Ray34. That has a 3 band pre-amp, and a better pickup (Alnico in the Ray34, Ceramic in the Ray4) and is a better quality build and wood. Not much more than what you'd spend on the pre-amp and pickup along with the value of your bass, esp if you bought a used Ray34.
If you're set on keeping your Ray4, then I'd say drop in a Nordstrand 4.2 pickup and their 2 band pre-amp. That's a very popular setup and upgrade to the Ray4 and should give you a great old school Stingray tone.
You are correct, it was a new ray4. A buddy of mine works at a guitar center and I got a good deal on it. All options are on the table but I thought I’d be able to come out in a good spot with replacing the electronics on this one. I’ll check out used ray34’s as an option too. Thanks!