hi, I do a small mod on my 308SW.
yesterday I got an active sub, the stock one taken from Mazda6.
This is really cheap option, 60 EUR including wires and connectors.
I Plugged it into lighter front socet. I plan to finish it over the wekend.
Now I fight with the speaker wires, my plan is to connect from the rear speaker.
I will let you know the results.