I’ve spent all of five minutes looking at your manual (so take this advice for what it’s worth) but having just did this install this past weekend I think I have some insight.
You need to connect the wires as show in the manual pic 1 (See attachments) not those in manual pic 2. That would be the White and Gray wire sets (with and without black stripe). If you use the RCA plugs, you are wiring up the pre-amp output which is “reduced” to be “amped up” producing a clearer signal. As you pointed out, you only need to hook up the front speakers on the base as there aren’t any rear. My info is from my Roadster base install, but I think it applies to what your doing.
Hope that helps
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