New split AC System impact on sound.

One benefit of variable speed systems is to address the very issue that you are concerned about, humidity. Those systems will run longer but, at a reduced (varying) capacity to have more time to wring moisture out of the air. I suggest that you put your contracter on the grill to get them to fully explain all of the pros and cons of these systems to help you make the best choice for you.

Yes indeed, oversizing an a/c system will result in reduced comfort meaning you will have cold but, damp air.

After 40 plus years in the a/c business I at least learned that the above is true. 

@tomaswv 

 The one thing I regret is not having insulators put between the compressor and the concrete pad on which it sits. 

You could still do this. 

Im a builder for 35 yrs.. The new compressors with heat pumps will have zero impact on your system. Get the variable stage. The most important factor on your audio system, sound wise, would be to have a dedicated 20amp circuit directly to your panel. You then avoid any possible high voltage surges like when a compressor kicks on. Cheers. 

Forgot to address the power issues.  Major appliances plus seasonal variability cause your AC to fluctuate in ways a dedicated line won't solve.  I've been watching my incoming AC for at least a decade, in apartments, condos and now a detached home.  I'm also paranoid about surge damage.  For these two reasons I recommend the Furman units with built in voltage regulation like this 15A unit or this 20A unit.  I also have a mostly dedicated AC line, with the exception of an attached internet camera.  The voltage sags and variability are NOT caused by my gear but by my HVAC especially in the summer.   Worth shopping around as some pro stores sometimes run amazing sales.

I think the main problem with oversizing your AC/heat pump is if it’s bigger than the house requires, it cools your home too quickly and cycles on and off too much instead of running for a longer duration.

Right, and these short cooling cycles are not long enough to run enough air through the radiator that captures the moisture. I think. And yes to the long term wear and tear.

Trouble for me is that the size needed for my home has just changed over the past 5 years I've lived here.  My risk assessment has gone from primarily flood and water to heat and wind.