shifting soundstage>

thanks for the test CD suggestion. the recording is certainly a leading suspect which is why I am wondering if many others experience the same malady with high quality recordings. If it is related to the recordings, I would expect that many are experiencing the same observation.

It is the recordings. A soundstage of an audio system does not shift back and forth; it is a set of components that operates within strict parameters. Unless you move the speakers, change gear or cables, it is fixed.

If the movement is so pronounced that it is unmistakably not the recordings, then you have a bad component somewhere in the chain.

There is another possibility; you could have something amiss happening with your hearing. 

Movement is slight and subtle, but the soundstage is normally very focused and dimensional making the shifts noticeable to me.
Regarding my hearing, a valid question since I am 80 years old. But, if I can hear those subtle movements, how bad can it be?

Try reversing the speaker leads on one speaker and see if that corrects the problem!

the speakers are in phase.