Imaging Demo Songs?

Check out Mapleshade CDs. Their recordings are specifically designed to do this well.

On the vintage side most look at Mercury Living Presence label recordings on vinyl or CD.

Surprisingly, mono recordings are useful for this. Generally a well focused yet ambient central presentation of a mono recording of any acoustic solo instrument including voice is usually a good omen that stereo imaging and soundstage will happen well. A murky, nebulous or unfocused mono soundstage is the opposite, a bad sign. Any good quality mono CD or vinyl recording might be used.

Why don't you list several popular CDs or LPs that others may have as well and then we can recommend what songs to listen to.

You have never done this yourself when things were working well??? You must have some favorites that you have listened to for years and know very well right? Try using those.

Opus 3 - Test Record 1 - Depth Of Image . Very fun to listen to.

Try some pink floyd, maybe the wall, or Wish you were here

Echoes is a good one from Floyd for this.