Welcome to the forum!
I wish that I found stuff like that in my garage.

I'd suggest that you do a Google search for info on that - only because there's some good info out there. Two of the first hits from my search are
here and
here. Looks like a very nice unit.
Regarding the subwoofer, there's likely a way to get it connected. The best way will depend on what kind of connections are on the subwoofer itself. What model is your subwoofer?
For other readers, here are some pictures of that receiver: