cd's/SACDS to test highs?

Just listen to a range of music you like. You'll know pretty quickly if the ribbons are more extended and sweet than what you're used to.

For me female vocals, cymbals and violin are the litmus test for highs.

I always listen to Rachelle Ferrell's "first instrument" for female vocals. There are many excellent SACD's with very well recorded solo violin (e.g. Bach partitas), and numerous Jazz trio recordings with great cymbal work (Lenny White is usually quite busy on the cymbals).

Edorr, Rachelle Ferrell "First Instrument" is excellent! Try Dianne Reeves "I Remember."

Use regular music to test your speakers. Listen to how well the ribbon tweeters integrate with the other driver(s). The high frequency range of the ribbon tweeters should be smooth and continuous with the rest of the frequency range of your speakers.

I own a pair of speakers with extended range ribbon super tweeters and was cautioned by the manufacturer not to use high level high frequency test tones with them as you can easily damage the ribbon tweeters that way.

There is a song on Moody Blues "Days of Future Passed" that has probably one of the highest notes that I've heard in a song. I believe it is "Evening Time to Get Away". It floats back and forth between the right and left speaker a couple times throughout the song. I only have it on vinyl. I can only imagine what the SACD would be like. The ribbons on my Infinity speakers throw that note out like its coming from behind the listener.
Have fun, JD