CVO Street Glides have a different amp setup from the Ultra--at least that's what I think.....maybe I'm wrong....
You are not wrong, CVO BOOM ll is a completely different setup. The Boom radio has front and rear outputs, fron to front amp, rear to rear amp. Each amp, front fairing & rear saddle bag on a CVO Street Glide is powering four speakers per say. Each speaker unit on the BOOM ll system is actually two separate speakers, a mid range and tweeter and a bass speaker which is using two channels of each amp. The amps, both front and rear are both 4 channel, 75 watt per channel amps. So two outputs to the right side front and two outputs to left side front are from the fairing amp and two outputs to the right side rear and two to the left side rear are from the saddle bag amp.
HogTunes is installing 6 speakers total using the radio rear outputs to power the rear and the radio front outputs to the Amp to power the front and lowers .
Where the OP is going to get the additional speaker outputs from or radio outputs for an additional amp, Good question.