Thanks again Matt.
Okay, so a somewhat frustrating evening, but mostly successful.
I was hoping I could use the digital optical cable from the onboard Realtek ALC898 chip to send 7.1 channels to the Marantz (3 bedrooms and the garage), then use the front R/L from the analog output to send to the Patio zone. The Realtek chip claims "7.1+2 CHANNEL HIGH DEFINITION AUDIO CODEC WITH CONTENT PROTECTION", which sounds like I should be able to send to 5 zones from this one chip, which is perfect.
However, I was never able to get the digital output to send more than a stereo signal. I disconnected all other analog connections, and created a zone to just send 5.1 and/or 7.1 output to the Marantz, but it only ever showed a stereo signal. I tried every combination of settings on the Marantz (auto surround, source direct) and only ever saw stereo. I tried changing the setting in the driver to NOT force front and back outputs to output the same signal, and that actually opened up another audio output option, limited to stereo (which would be fine, since i'd just use that for the Patio), but still only ever received Stereo at the Marantz.
I eventually gave up and used the analog outputs to send to the 7.1 input on the Marantz, and got it working as described. Unfortunately, I only have 2 3.5mm 'splitter' cables to go from the board to the receiver, so I can't test that it works for all 8 channels, but I assume it will.
Sadly though, I discovered another 'flaw' in the plan, which is that although the Marantz offers 7.1 channel input, and supposedly offers 7.1 channel output, it achieves that by not sending an amplified signal to the subwoofer, and only sends one amplified output to one rear surround, with a pair of pre-amp outs if I want to use 2 rear surrounds, which then need their own amplifier. So, I can still only send amplified signals to 6 speakers thru the Marantz. So, I have to find another way to power the 4th zone. I'm thinking this will be done by connecting the garage and the patio speakers to the same terminal on the Yamaha AVR Zone 2 output, since I can turn that zone with my phone. This would mean I'd have to have both zones actually playing music when using either zone in MC, but I don't have any other amps I can use and a 2 channel amp is over the cost/value limit in this case. I've thought about a car stereo amp, since they seem way more affordable, but I'm guessing it brings it's own problems
Also, by having to use the analog outputs to get the 4 zones working, I don't have any way to send a separate, 5th signal to the Patio, unless the front output can actually send a different signal than the rear outputs, and even then, that means an ugly cable sticking out the front of the HTPC
Maybe someone has some experience with this common Realtek chip, and can help me get the optical output to work for 7.1 and I can use the rear "Front L/R" analog for the Patio, like I have been doing thus far.
I suppose if push comes to shove, I'll just have one zone in MC for the patio
and garage, since they will probably be connected to the same amp output, but I'd prefer to keep them separate if possible.
Thoughts/suggestions/feedback welcome