Surround sound

A lot of receivers also have a "dialog enhancer" mode, which basically boosts low-level audio signals to the center speaker whilst leaving the high-level signals alone, at least in the speech frequency band of up to 3KHz.

However from the description of your wiring setup, it seems you are only using stereo connections to your 5.1 receiver. Thus you need to select 2-channel (not 5.1) audio output from your BD discs, and also set your receiver to either 2 channel output or simulated surround-sound (which emulates 5.1 output using a 2-channel input).

If your receiver has at least one HDMI input & an HDMI output, use those to connect your BD player to the receiver and the receiver to the TV. If not, then get an optical cable to connect the BD player to the receiver for true 5.1 audio. In either case, I'd agree with soundguruman that you need to adjust your speaker outputs for the best listening experience at the seating location you most commonly use when watching movies. Many AV receivers include a microphone that you place at the normal seat positions and automatically calibrate the speaker output.