lowoverdrive- Welcome! As the responses to the OP amply demonstrate, if you ask a question like this to 4 audiophiles, you will get 6 or 7 different answers. You have done a good job of responding and describing the results of your experimentation so far. Issues like break-in and cabling should not be the source of overwhelmingly harsh high frequencies. Here are my observations, some of which align with yours:
1. That is a lot of speaker for a small room. You are listening in the near-field and that speaker is not designed for that.
2. One review I found noted a forward sound with sharp attacks and an edgy sound. Another review said that could be a bit harsh. A consumer review said they were for "treble lovers only". In the near field with modest electronics, that could easily be perceived by someone else as a fatiguing harsh treble.
3. The speaker is also described as requiring lots of power to open up. The receiver has been measured to provide only 65 watts/channel at 0.1% distortion. If that distortion is of the wrong kind, 0.1% can easily be very audible as harshness. Solid state amps that use feedback to keep the measured distortion low often create that kind of distortion.
4. Your small room has two very large glass reflective surfaces (TV and computer monitor).
In sum, you have inadvertently created a sort of positive feedback loop; positive in the sense that all of these factors contribute to the sound quality you described, with an overemphasis on the treble. You found that changing the speakers helped some. You also noted that the AVR and small speakers are quite adequate for movies, and asked about using the larger speakers with different electronics in a larger room for music.
That is probably the best solution because you probably cannot change enough of the factors that re-inforce each other in that small room. Modest priced AVRs generally "sound" like they have less than their rated power when playing music and have much of their $$ allocated to digital signal processing, auto-calibration, and the gazillion input and output jacks/plugs/ports on their rear panels. If you cannot return the large Polk speaker, then I would look for electronics known for a warm or slightly laid back sound (often described as a British sound) and put them in a larger space where the speakers can be well out from the wall behind them and where you can place furniture/pillows, curtains, etc to break up reflections and enhance diffusion of the sound. If it's just for music, an integrated amplifier might be a good cost-conscious solution. If you give us a budget and whether you want to buy new or used, we can make specific suggestions.
1. That is a lot of speaker for a small room. You are listening in the near-field and that speaker is not designed for that.
2. One review I found noted a forward sound with sharp attacks and an edgy sound. Another review said that could be a bit harsh. A consumer review said they were for "treble lovers only". In the near field with modest electronics, that could easily be perceived by someone else as a fatiguing harsh treble.
3. The speaker is also described as requiring lots of power to open up. The receiver has been measured to provide only 65 watts/channel at 0.1% distortion. If that distortion is of the wrong kind, 0.1% can easily be very audible as harshness. Solid state amps that use feedback to keep the measured distortion low often create that kind of distortion.
4. Your small room has two very large glass reflective surfaces (TV and computer monitor).
In sum, you have inadvertently created a sort of positive feedback loop; positive in the sense that all of these factors contribute to the sound quality you described, with an overemphasis on the treble. You found that changing the speakers helped some. You also noted that the AVR and small speakers are quite adequate for movies, and asked about using the larger speakers with different electronics in a larger room for music.
That is probably the best solution because you probably cannot change enough of the factors that re-inforce each other in that small room. Modest priced AVRs generally "sound" like they have less than their rated power when playing music and have much of their $$ allocated to digital signal processing, auto-calibration, and the gazillion input and output jacks/plugs/ports on their rear panels. If you cannot return the large Polk speaker, then I would look for electronics known for a warm or slightly laid back sound (often described as a British sound) and put them in a larger space where the speakers can be well out from the wall behind them and where you can place furniture/pillows, curtains, etc to break up reflections and enhance diffusion of the sound. If it's just for music, an integrated amplifier might be a good cost-conscious solution. If you give us a budget and whether you want to buy new or used, we can make specific suggestions.