There appears to be no rhyme or reason to Yamaha's audio wiring, nor limitation on their ability to screw it up. Please take a look at the following thread, particularly post 6. It will give you an idea of how hard Yamaha biffed the factory wiring on my 212X in 2018. I spent a LOT of time trying to straighten it out just to make it sound like it should from the factory.
I know at least one late year 2018 242X owner whose speakers were wired in parallel, an indication that Yamaha was starting to get its act together on how to hook this stuff up.
As far as figuring out how your setup is wired, I think that's a good place to start this project. You can tell if you're in parallel or series by pulling one of the wires off the back of one of the bow speakers when you remove it. If another speaker stops playing (like the same side cockpit speaker), the bow speaker is wired in series with it. If not, either the bow speaker has its own dedicated channel or is wired in parallel with another speaker. Think of old school Christmas tree lights where, if one light is unscrewed or burns out, the entire string no longer lights. That's series wiring. If you can remove one light and the rest stay light, they are wired in parallel. Same thing with these speakers.
As far as how I wired my setup, I was adding an extra amp anyway (I've now added two extra amps), and I had enough channels to give each speaker its own. If I ever decide to add more speaker, I can easily double up two sets to free up some channels. But bear in mind, wiring them in parallel provides 150 W/channel to two speakers, whereas wiring them on their own channel provides 100 W/channel available per speaker.
Also, bear in mind that your amp is an HTX-6 DSP--which does not use the traditional RCA inputs or single wire output lugs. It also does not have user-accessible tuning controls. Instead, it uses proprietary connectors and all adjustments are made via firmware. So, it's not as simple as moving wires around. You will see when you take a closer look at your amp. If you are OK with how your system sounds now and want to simply add more speakers and another amp, you might try to do that independent of messing with the OEM amp. I ended up swapping mine out for the non-DSP version of the amp, but that was due, in part, to the fact that the Yamaha had completely failed in their attempt to wire my system together at the factory. I pretty much needed to start from scratch. Here's another thread, which, in addition to discussing adding mid cabin speakers, goes into some detail about what I was dealing with with Yamaha's OEM wiring (that part is further down in the thread).
We picked the Rev 8's rather than the Rev 10's based on balancing sound and space considerations. We tried to figure out what would best fit in the space, without worrying about hitting our heads on it or otherwise being in our way. Combined with the soundbar, the Rev 8's seemed to be the best way to go for our application. But I could easily see choosing the Rev 10's instead.
Jeff
