Tonight I attended Mass at Mater Ecclesiae, where the Rector, Fr. Robert Pasley, as he likes to do from time to time, made use of the tonus solemnior for the Preface-Canon. This is the "more solemn tone," which, as you have probably surmised, is even more ornate than the Solemn tone. It is truly a work of musical genius which calls to mind the phrase from the Psalms, "sing artfully unto God." This melody is one way to bring special music right to the very heart of the liturgy. In fact, tonight it was the liturgical highlight of the whole ceremony. If only I had gotten a video!
Of course, this complicated liturgical gem must be performed with the utmost care, and tonight the good rector delivered on this, per usual. I may sound like I'm trying to win favors, but I beg you to believe that I speak the truth: Fr. Pasley should be teaching priests and seminarians how to sing all over this country. We must make him famous! His skills in the vocal art are unmatched by any other priest I have ever personally known.
I believe that this tone can be found near the back of the 1962 Missale Romanum. My understanding, however, is that it is not in all the Missals of the Traditional Rite, so it might be a bit tricky to find at first. The Missal which the CMAA has posted online for free contains it. Be careful, though: that's a big file.
Now that the summer hiatus is upon us, perhaps those priests who think this is something they'd like to learn should start looking at it. If one spends a modest amount of time with it from now until August, it could probably be in first-rate shape by the Feast of the Assumption, or, at the very least, by Christmas. And, by all means, if you need help, ask. Most of us church musicians would be quite eager to help you.
One practical note: For the dialogue portion of the Preface, it might be most wise, at least at first, to use the Solemn Tone, and then jump into the Tonus Solemnior after the dialogue portion is complete. This is for the sake of the congregation. Surely, if one were to use the dialogue portion of the Solemnior, the congregation would need the notation, at the very least.