Best way to connect Controller FLX4 to Bose S1 Pr0

Greetings,

I am using a RCA to quarter inch pin to connect to my Bose S1 Pro. However, it takes away a lot of sounds effects away like the Drums and snairs. Sounds very wierd. It sounds fine on the computer speakers, but not on the Bose S1 Pro. Can you please help.