This project, service.odroidn2.oled by roidy, looks quite useful!
https://github.com/roidy/service.odroidn2.oled
It doesn’t have the spectrum display, but the info display is quite nice. It’s for an Odroid N2, driving via I2C. I think that should easily port to either a C2 or C4.
Discussed here on this thread:
https://discourse.coreelec.org/t/odroid-n2-oled-i2c-spi-driver/4995