If I were to use the splitter I figured I’d want to use two bass amps for though
Assuming the previous owner hasn't snipped it, the "Treble" (bridge) pickup has a capacitor that filters out low frequencies, as it's designed to safely feed a guitar amp / speaker.
That capacitor often got removed, to restore the bass frequencies, and make the bridge pickup useful in it's own right.
Even if you can't be bothered to cart an additional amp & cabinet around for live gigs, Rick-O-Sound is still great for recording.
Additionally, any 2 channel amp that allows you to bridge the channels together, should enable you to put the neck pickup through the normal channel, and the bridge pickup (with any distortion, chorus etc) through the bright channel.
Of course, you loose the biggest advantage : spatial separation. But you do at least gain a more controlled parallel effect.
I actually have an old Marshall bass amp, that features a normal channel, a bright channel, and an additional stereo input that takes the signal from the treble pickup on the Tip of a TRS lead, and feeds the bright channel. It takes the signal from the bass pickup on the TRS Ring, and feeds the normal channel.
As others have mentioned, do your homework
before adjusting Rickenbacker truss rods.
The other thing that I don't think has been mentioned : older 4001's used soft fret wire, and were intended to be used with flat wound strings.
Assuming the previous owner has treated it right, you probably don't want to start using stainless steel round wound strings (afraid I can't remember which year Rickenbacker started using tougher fret wire, so ask around on the Rickenbacker club here, or Rickenbacker Forums what is safe to use).
