Op,
Well, honestly this is pretty budget gear… and typically if it fails… it fails with the result of a lot of high frequency hash.
The volume control should satisfy your wife if the sound does not have a lot of high frequency hash (women tend to be much more sensitive to this). Typically good quality electronics will get rid of the problem… but I think speakers would be your first best bet.
I would start by looking for higher quality floor standers. Like Totem, or Sonus Faber… not B&W. You want warm and punchy. But consider spending some money on them (like a couple grand). I think you are stuck between consumer and high fi.
Since your amp has a streamer… switch services to Qobuz. It is a audiophile service. Then you can be sure the in-ut is good. Apple is not great.
if all this fails… then you are going to have to upgrade the lyndorf.