Thank you for the wonderful feedback. This makes me want to ask you a few things. First, how would I tell about my receiver being bright or I think you meant, harsh?
Secondly, when you bought your Polk A3's, did you know if they were more of a home theater type speaker or for music as well?
This is far from scientific, and completely subjective. First off, since I am not listening to your Onkyo on a daily basis, it is not fair for me to assess its sonics. However, there are things I personally listen for when determining components character.
Assessing Brightness: Is determined two ways. One, is not only do I listen to music, but bring something that has some spoken word. What I looking for is overly pronounced S and T sounds. (AKA spitiness) Telarc
Symphonic Star Trek is an example. Then ask, does Leonard Nimoy's voice sound clear and natural?
The second, is I also bring something "close miked" like Allison Krauss's
Forget About It and listen for the same thing. Does this piece of gear make it sound as if she singing into my ear or is her voice seem like it's hissing?
( Be advised, this coloration can show up in recordings, music sources, amplification, and speakers. So it might take switching out of components before isolating which piece of gear has it.)
In regards to Hash: How it manifests itself for me, is when a instrument that is not electrified takes on an electric, amplified, guitar sounding character. This usually shows up at higher volumes on music that has loud peeks. I like using something that features a piano being performed solo, or in a duet. George Winston or Robert Silverman (Stereophile's
Poem) type stuff. When listening on a loud passages, where the performers are hitting those ivories with a lots of energy, does the piano still sound natural, or has the sonics taken on a sort of crackling, an egg is frying character? There is not really an audible pop (Clipping ) or horrible notes (Distortion) emanating from it, but the instrument is no longer sounding 100% realistic and organic either. In short, is a $50.000 plus Steinway, now sounding like a slightly broken $500.00 electric KORG?
If an component has either of these sonic characteristics, Polk speakers bring that out in spades.
I knew that Polk primarily produces home theatre speakers now days. That used not be the case 20 years ago. That being said, I had enough positive experience with them to know they can be very musical when matched with the right gear. They are well acclaimed for good reason and have not abandoned their 2 channel music heritage. After all, if a speakers does well with music it will also do well with movies. Klipsch still makes what I consider "High End" speakers specific for 2 channel music. Sadly those are expensive, starting at $2K and up. Nonetheless, that technology trickles down to the model you are considering, which is another reason why I think they would be a better fit than the Polk Audios.