I don't know for sure on your 2009 Suncruiser. But on my 2017 Adventurer (the Suncruiser's Wbgo cousin) it's built into the BluRay DVD player. It's an all in one unit and all the speaker wires are connected on the rear of the LG brand Player.
I'm sorry I don't know if this has any relevance to your 2009 model, but I hoped by mentioning it that it could help your search.
UPDATE:
Your Operator's Manual seems to indicate you have an Optional DVD Home Theater system. So, I'd guess that's where you'll find your speaker connections.
Operator's Manual Link:
https://www.winnebago.com/Admin/Publ...Suncruiser.pdf
Entertainment Section - 8-5