Can any one explain why the sound is bright and lean?
Since I don;t know the characteristics of your AV rec (is there an input buffer...etc?) or yr source, I can only surmise that the source component is NOT outputting enough energy to drive the receiver.
You should try connecting the TVC to a power amp and check.
Transformers do break in -- but the most usual/immediate and perceptible improvement is in the resolution /hi freq. Cheers