Learn English – What does “for” mean in this sentence

I think the meaning is close to your first suggested interpretation. I would word it as:

Now we are about to hear the music we have chosen for today.

The two-word phrase here comes is somewhat idiomatic, meaning "something or someone is arriving at or approaching the place where we all are now." There's a song often played at weddings that begins with "Here comes the bride..." which means, essentially, "The bride is here!" Similarly, "Here comes the bus" implies the speaker can see (or hear) the bus off in the distance. So, when the speaker says, "Here comes the music today," I interpret that as, "Today's music is about to be heard."

It might be worth noting that the last paragraph isn't very well written. For the most part, "music" is an uncountable noun, so I'd offer this suggested edit:

I shall explain why they are all good songs... (or compositions, perhaps)

or:

I shall explain why it is all good music...

In this particular example, 'than before' is a shortened form of 'than they were before.'

NOTE: The example statement tells nothing about what the other half thinks. Some of the other half may well have no opinion and assumptions about what they think are invalid.