Personally I'd say look for some pickups from a MIM Fender bass. Ebay or this forum may have some. People swap out the pickups on those all the time, and in my experience the MIM pickups are pretty nice - certainly much nicer than the stock pickups in your SX. You can usually pick up used stock pickups for almost nothing.
The stock pickups on most SXes that I've played are competent pieces that sound decent, but stock MIM pickups are a definite step up.
I did that for my Squier Affinity P-Bass. I got a MIM P-Bass pickup on eBay for $5.00, and I was the only bidder, which surprised me, since they're good pickups - not great, but good. Better than what I had on my Squier, that's for sure!