six-piece Dixieland band

[masterding]

Quotes from VOA News:
"Choir and Dixieland band, now there's an interesting combination," says Childers. "I thought, 'Well, I don't know of any music written for that combination - certainly not a Christmas piece other than traditional carols something like that.'"
So he composed seven original songs to be performed by the choir and a six-piece Dixieland band, with Childers on the trumpet.
The result is a blend of jazz, swing, ragtime, blues and more than two-dozen harmonizing voices.
The songs tell the story of the birth of Jesus. "Gabrielle" speaks of the angel who comes to Mary and announces she will give birth to a son. "Go and Find the Christ Child" evokes the shepherds' quest to follow the star to the manger where Jesus was born. And then there's the "Manger Blues."
My questions:
1.I understand the first half of the sentence, but I don't quite understand the second half after the punctuation.
2. What does "piece" mean here?
3. What does "speak of " mean?
Thanks!

[5jj]

In a six-piece band, there are six players. Often (but not always), each player plays one instrument only.
'Speak of' is similar in meaning to 'talk about' in this context.

[masterding]

In a six-piece band, there are six players. Often (but not always), each player plays one instrument only.
'Speak of' is similar in meaning to 'talk about' in this context.

Then who is "Gabrielle" that talks about angel?

[5jj]

"Gabrielle" appears to be the title of one of the songs, so 'tells us about' is perhaps better than 'talks about'

Christmas Concert Hits Jazzy Note | Arts & Culture | English