What JimmyM said.
I started playing with my dad's band, the original bass player, Tony Pe'na, (tony, you here?), would plug my bass alongside his into the SVT 810, and I would play along, learning the songs, when I got it down he would smile and put his hands up to show I was doing it. Eventally he would get drunk and fall over, so he trained me like his padawan, and quit the band.and that's how I started playing biker bars at 15.
But strange phase things happen, you couldn't gig like that, you cancel each others signal s out.
Get another rig. Two basses is wonderful, I want more players to do it. And not cheesy 1980's bass battles (never lost one tho!) But proper harmony, try playing the third, look into vocal sheet music, beatles especially for good 2 bass harmonies.