Hi @Jwinebrenner, welcome to the Sonos Community!
There are three Line-Out Level options; Fixed, Variable, and Pass-Through. With the Variable Line-Out Level option, there is some signal processing when enabled to allow for the Sonos App to control the Ports volume and send this to the connected amplifier. This isn’t present on both Fixed and Pass-Through as the Port is on a fixed volume on these options. It’s likely that the persistent static you hear is the extra signal processing that is coming through which your McIntosh MA5300 isn’t expecting.
While Fixed doesn’t let you use the Sonos app to control the amplifiers volume, you should still be able to control the volume via the Sonos app with Pass-Through. With this enabled, Pass-Through will send volume commands from the Sonos app to the amplifier as if you were issuing the command to the amplifier itself, though this will only work is your amplifier supports Pass-Through.
If your amplifier has a Pass-Through option, I’d recommend enabling that so you can use the Sonos app. Otherwise, you’ll have to control the volume from your McIntosh MA5300.
I hope this helps!