Atermarket stereo harness

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I was browsing Cruthcfield and noticed instead of message that said: "u will lose center and rear speakers" and "splicing into factory harness required" it now reads: "Your vehicle is factory-equipped with an upgraded sound system. We recommend that you purchase an adapter that will connect your new stereo to your amplified factory system.
Scosche Lexus/Toyota $149.99"
What is that adapter, and will I retain all JBL speakers and steering wheel audio controls?

 

[p nut]

I have no idea, but the best thing to do would be to call up Crutchfield. I have called before and they were really helpful and knowledgable.