When using the PLD4.5 with 4Ω in 2-channel mode, you can get the best sound by setting it to "AB or CD parallel mode" instead of "A+B or C+D bridge mode".
Below is the Power Specifications table from the product page of the manufacturer site. There is a description NR (Not Recommended) under the PLD4.5 column for 4Ω in "A+B or C+D bridge mode". In "AB or CD parallel mode", a large output of 2250W (4Ω) can be obtained.
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