I don’t think you have the speaker outputs connected correctly. If you have the positive phase corrected to one input and the negative phase connected to the other, you want to connect the positive speaker wire to the positive terminal of the channel that is connected to the positive phase of the balanced connection, and the other speaker connection to the positive speaker terminal of the other channel. The negative speaker terminals from both channels are connected together as you have them.
This is known as a bridge tied load.
This kind of connection can only be done with amplifiers that are not already bridge tied loads which generally means the negative speaker terminals are connected to signal ground.