Nice answer as always! In my case, I send all the frequencies below 80Hz to the subwoofer which helps with the distortion of my KEF R500 woofers and load on AVR. Unfortunately, KEFs impedance drops down to 3.8 ohms between 120-160Hz and AVR has to work with that load. Noise in my room is around 34dB average SPL C weighted / 26 dB SPL A-weighted. I'm going to add some mass-loaded vinyl to cover my windows to see if I can bring it down a bit.
I think anyone who listen loud with the R500 really should at least use an online calculator to estimate the actual power need. It is not the 3.8 Ohm in a narrow range you need to worry about, but the fact that it stays below or at about 5 Ohms in a wide range 80-1000 Hz, that's more than 3 octaves. The saving grace is, the phase angles is that range is benign. Even the X4700H can drive them, depending on distance and spl listened to. Regardless, an external fan should be used imo.
Crown Audio - Professional Power Amplifiers
Edit: As bigguyca said, I should have include the following link, please read before using the Crown calculator.
How Much Amplifier Power | Crown Audio - Professional Power Amplifiers
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