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I don't see an - Impedance Switch - on the Denon DRA-900H Receiver https://www.crutchfield.com/p_033DRA900H/Denon-DRA-900H.html If you are not getting the Dynamics you want at low Volume, then Tweak the Bass and Treble upward a bit. Generally, you lose Bass and Treble at low Volume. This is what a Loudness Switch does, it gives a slight Bass and Treble Boost at lower Volume. Though True Loudness Switches are Rare today. As to the - Impedance Switch - if it had one, just leave it on 8 ohms and don't abuse the Amp (volume wise). I have a Yamaha Receiver that has an Impedance Switch and it has been set to 8 ohm for years, decades really, without a problem. And During Movies, I've hit some pretty Stellar Peaks. I believe I was measuring one time during a Movie and the SPL Meter Pegged at 110dB VERY Briefly. As mentioned by others, to meet Consumer Regulations, the Impedance Switch just lowers the Voltage on the Power Stage to keep the Regulators happy, but in daily use, it is pointless. Unless you are playing at Demolition Volume Levels, leave it at 8 ohms. Also, what is the - Source - of sound you are listening to when you experience this problem? CD? Streaming? Bluetooth? Turntable? Other? If it is Bluetooth, then there is your problem. If Streaming, depending on the Service you are using, that could be a slight problem. Also, Speakers on at Cabinet Top is not the best. If you do this, move the speaker so the Front Edge of the Speaker is even with the Front Edge of the Cabinet. In your case, though it might simply be perspective, it looks like near Speaker is farther forward than the far Speaker. They should both be up to and perhaps a trace over the Front of the Cabinet ... in my opinion. You can get Short Speaker Stand meant for use on Cabinet/Table/Desktop to raise the Speaker off the broad flat surface. Examples - https://www.amazon.com/Rockville-Resonance-Free-Management-Isolation-Bookshelf/dp/B07PV9WXSK/?th=1 https://www.amazon.com/gp/aw/d/B07VL6DTDR/?th=1 https://www.amazon.com/Suptek-Universal-Desktop-Speaker-Stands/dp/B0FWB4F58V/ https://www.amazon.com/Desktop-Speaker-Compatible-Bookshelf-Tall/dp/B0FM8KKSFM/?th=1 These are just random examples that came up on quick search. Also, consider the General Acoustics of the Room. From the single picture I can't make a determination. It doesn't look too bad. But Room Reflections and really mess up the sound.