Hi Samuel,
So the Luxe is using an audio codec chipset to manage many things like volume control or input output selection, and commands are sent to the codec in I2C. So unlike the PROTO the LUXE needs to send commands to the codec to start playing.
I advise that you start with the Arduino example for the luxe that could be found here:
All pin definition should be found here too 
Simple_Bluetooth_Speaker_ESP32/speaker/speaker.ino at master · RASPIAUDIO/Simple_Bluetooth_Speaker_ESP32 · GitHub
so for the SD card :
#define SPI_MOSI 15
#define SPI_MISO 2
#define SPI_SCK 14
We will document the LUXE better in the next days, your are one of the 20 first owner of this product.
Cheers