It should be an EMG BTS circuit inside, so you have passive pickups with an active circuit. Upgrading the pickups to full active EMGs is something I tend to do, but if you're happy with the Hz pickups why bother, as you say?!
It's worth flicking the two tiny mini switches on the BTS into each combination of 'off' and 'on' to see which sound you prefer. I, and many others, like having both switches 'on' for a more biting Spector tone, but playing dub/reggae etc you may find a different combination preferable. Enjoy experimenting!