I either use the PO’s built in speaker or have to use My guitar amp set to play quiet.
For monitoring? I have some equipment that I use for guitar or iOS instruments - haven’t tried it yet, but plan to run one or more PO’s into a $50 Mackie 5-channel mixer, and then the output of that to a pair of M-Audio BX5 monitors. So that’s a relatively cheap home setup that works for my purposes.
If I want to hear things more quickly, I have a Yamaha THR10 and Blackstar Fly3 - both are mini amps with AUX jacks for external output. The THR10 actually sounds pretty good, but for bass and drums there are obvious limitations using speakers that small.