2007 CTS-V: replacing the stock head unit with an aftermarket nav unit and adding a sub, but I want to retain steering wheel controls, will this take care of it:
or is there a separate piece? I've searched and I can't seem to find any specific link or information anywhere.

Main reason is a local shop quoted me around $500 for all the needed parts and install if I brought just the aftermarket nav unit, trim piece and install kit, and the all in one powered sub unit. I can use my own parts but if they're not that much less expensive I'd rather take their parts and get the warranty if anything goes wrong.

Thanks for any info/advice!