You are correct the radio only controls the outdoor speakers. You can connect to it via blue tooth and play from your phone or use it as a radio. If you go to Furrion's website you can download operation instructions and read about the systems capabilities. A subwoofer can be hooked to it which will improve the sound quality but you can't play them very loud anyway without disturbing others around you.
2018 Redwood 3901WB pulled by 2016 Chev 3500 HD DRW. Goodyear G114 tires, Moryde I.S., Kodiak Disc Brakes, Splendide W/D, Tire Minder TPMS, Sleep # King.