What is your evidence? I doubt it is literal stated fact. I can't imagine any electronics manufacturer deliberately skewing the frequency response curve. Having said that there can be factors that you might not glean from a review. One of these is source impedance. I suppose it is just possible that your new receiver has a higher source impedance, and may be following the impedance curve of your speakers. Bench test are done into a power resistor, which in not the same as speaker loads, which are all over the map. But I would bet that your receiver would test the same on the bench as all other similar devices. I suggest you experiment with external amplification.
Below is the FR measured by Audioholics, so the FR is not tweaked.
Lastly how many channels are you driving hard. These days there are too many amps in one case from one power supply. That receiver is an 86 watt per channel device seven channels driven. So if you are using high volumes, then external amplification is recommended.
