The series or parallel connection thing has been very confusing to me until well… Now. The reason why it’s so confusing is because so many sources online are confusing/just plain wrong. My manual for the pjb clearly states you can daisy chain the cabinets together IN PARALLEL giving you full power to the cabs. Yet a quick Google search states that daisy chaining gives you a serial connection which greatly robs you of power. So what gives? Well a few minutes ago I found this thread, which explains it:
TL/DR: it is very rare to find any cabs wired with a serial connector any more, they’re almost all parallel. So connect them however you want (after consulting your manual). Every time you add a cab you decrease the ohms. 1 8 ohm cab is 8 ohms. Add another and they are 4 ohms. Add another and you’re at 2.7 ohms, you can use an online ohms cabinet calculator. Most amps only safely go down to 4 ohms, a few do 2. Don’t start a fire onstage. I simply went output one to cab one, output two to cab two because pjb says it sounds a bit better but in the real world with 2 foot cables it probably doesn’t matter. BTW @DaveT here told me all the same things in a thread once.