Klipsch Reference Cinema 5.1.4 System with Onkyo TX-RZ30 Bundle | Dolby Atmos 5.1.4 Klipsch speaker system with Onkyo TX-RZ30 9.2-channel 8K receiver

https://a.co/d/0hwWEuGr

Those are are composite audio cables. That means your house used to have speakers in those areas or it could still have speakers in the walls. Big black box that they took was probably a old receiver if it look.domething like this https://a.co/d/08veqDw4