Yikes, I nearly forgot I was plowing through this document . . . at this rate, the new MCW will be out before I finish!
VI. Language for Use in Sung Liturgies; Preserving the Treasury of Sacred Music
47. According to the Constitution on the Liturgy, "particular law remaining in force, the use of the Latin language is to be preserved in the Latin rites." 
At the same time "use of the mother tongue . . . frequently may be of great advantage to the people."  Therefore "the competent ecclesiastical authority . . . is empowered to decide whether and to what extent the vernacular is to be used . . . The acta of the competent authority are to be approved, that is, confirmed by the Apostolic See." 
These norms being observed exactly, there should be a wise use of the kind of participation that is best suited to the capabilities of each assembly.
Pastors should see to it that, in addition to the vernacular, "the faithful are also able to say or to sing together in Latin those parts of the Ordinary of the Mass belonging to them." 
Well, I won't get into the conspiracy theories in regards to the demise of latin in the liturgy . . . but it really is a shame that this last little bit couldn't have been pushed a bit more in the last 30+ years. Though I can sing the "Pater noster" if I have the notation in front of me, I couldn't recite it to save my life . . . same with the Gloria (though I could do much better) and the Credo. Hopefully this can be somewhat corrected in the next couple of generations.
48. Once the vernacular has been introduced into the Mass, local Ordinaries should determine whether it is advisable to retain one or more Masses in Latin, particularly sung Masses. This applies especially to great cities in churches with a large attendance of faithful using a foreign language.
It seems that this is starting to revive itself somewhat throughout the country, especially since this universal indult may actually come to fruition. We have a latin mass once a month at my church (though it's on a Tuesday at 5 PM) which is a step in the right direction.
Of course, in a situation with many different ethnicities, it would be necessary for each person to have a missal in hand with the latin and their native language. Worship aides put together by the church would be a potential logistical nightmare depending on how many different ethnicities would be present.
49. The norms of the Congregation of Seminaries and Universities on liturgical formation in seminaries are to be observed in regard to use of Latin or of the vernacular in liturgical celebrations in a seminary.
The norms in the Motu Proprio Sacrificium laudis, 15 August 1966, and this Congregation's instruction on the language for religious in celebrating the divine office and the conventual or community Mass, 23 November 1965, are to be followed in their liturgical services by the members of institutes professing the evangelical counsels.
50. In liturgies celebrated in Latin:
a. Because it is proper to the Roman liturgy, Gregorian chant has pride of place, all other things being equal.  Proper use should be made of the melodies in the editiones typicae of this chant.
b. "It is desirable also that an edition be prepared containing simpler melodies for use in small churches." 
c. Other kinds of melodies, either for unison or part-singing and taken from the traditional repertoire or from new works, are to be held in respect, encouraged, and used as the occasion suggests. 
Seems like a hierarchy here: a) Graduale Romanum b) Graduale Simplex c) Other, which is sufficiently vague here.
51. In view of local conditions, the pastoral good of the faithful, and the idiom of each language, parish priests (pastors) are to decide whether selections from the musical repertoire composed for Latin texts should be used not only for liturgies in Latin but also for those in the vernacular.
Well, to fulfill the request that the faithful know the Ordinary in Latin, it seems that using chant settings during masses in the vernacular is a good idea, at least occasionally.
52. To preserve the treasury of sacred music and to encourage new styles of sacred song, "great importance is to be attached to the teaching and practice of music in seminaries, in the novitiates and houses of study of religious of both sexes, and also in other Catholic institutions and schools" and particularly in institutes of higher studies specifically established for this purpose.  Especially to be promoted are the study and use of Gregorian chant; its distinctive qualities make it an important foundation for a mastery of sacred music.
Yeesh, I'd say they dropped the ball on this one. I think just recently seminaries are making an effort to find adequate musical training for our future priests. A seminiarian at the Mount had told me that they just recently re-hired a Director of Music after a 10-year absence due to budget cuts. Yikes.
53. New compositions are to conform faithfully to the principles and rules here set forth. "They are to have the qualities proper to genuine sacred music; they are not to be limited to works that can be sung only by large choirs, but are to provide also for the needs of small choirs and for the active participation of the entire assembly of the faithful." 
I'd say it's safe to say that the writers of this document didn't have the music of Joe Wise in mind when they composed this section . . . (I apologize if that came off as uncharitable)
Those parts of the traditional treasury of music that best meet the requirements of the reformed liturgy are to receive attention first. Then experts are to study the possibility of adapting other parts to the same requirements. Finally, parts that are incompatible with the nature of the liturgical service or with its proper pastoral celebration are to be transferred to an appropriate place in popular devotions and particularly in celebrations of the word of God. 
This makes it very clear that the progressives were out-of-line when they felt that the council was calling for all "old rite" music to be tossed. On the other hand, it seems that the fathers wanted to do everything possible to salvage all quality music that was not incompatible with the new rite.
30. Sacrosanctum Concilium art. 36, §1.
31. Sacrosanctum Concilium art. 36, §2.
32. Sacrosanctum Concilium art. 36, §3.
33. Sacrosanctum Concilium art. 54. See Sacred Congregation of Rites, Instr. Inter Oecumenici,
26 Sept. 1964, no. 59.
34. See Sacrosanctum Concilium art. 116.
35. Sacrosanctum Concilium art. 117.
36. See Sacrosanctum Concilium art. 116.
37. Sacrosanctum Concilium art. 115.
38. Sacrosanctum Concilium art. 121.
39. See no. 46 of this Instruction.