Since you posted this in the Alerts section which is reserved for giving people a heads-up regarding items for sale that you’re not affiliated with, I’m going to say that those are a bit overpriced.
Coaxial is a digital connection. XLR is analog. Neither are going to introduce noise unless a component is failing.
If you go XLR, the upstream component’s DAC will handle digital to analog processing. If you go coaxial, the downstream component’s DAC will handle the digital to analog processing. For me it would depend on which component’s DAC was superior.
Yep. Loosen and tighten every screw on the input terminal and on the crossover network. It’ll remove years of oxidation and give a much better signal path.
Things like dynamic volume, dynamic EQ, anything along those lines. Generally when you disable anything like that things will sound better. Also, it might help to increase the center speaker output a couple dBs.
Very unlikely that the speaker is defective. There’s lots of settings in your receiver that you’ll want to mess around with to tailor the sound to your liking.