If you're looking to hook up your bluetooth adapter or a 3.5mm to RCA input to a 4 channel amplifier you'll need one of these splitters. This will allow you to split the signal coming from your source and feed all four channels of the amplifier.

If you would like too hook up a bluetooth adapter and a 3.5mm to rca adapter then you will also need two RCA Y Adapter (2 Female 1 Male) adapters!

Wiring Diagrams

Single Source to 4 Channel Amp Wiring
3.5mm AND Bluetooth to 4 Channel Amp Wiring