1)
Why does it say "ba'Shir Lo Yishtu Yayin"?
1.
Radak: The way of revelers is to drink amidst singing. They will sigh; there is no song in their mouths.
2.
Malbim: Not only did songs with musical instruments cease - they will not even sing vocally while drinking wine.
2)
Why does it say "Yemar Shechar l'Shosav"?
1.
Radak: The little strong drink that they will drink will be bitter in their mouths, amidst many Tzaros.
2.
Malbim: Strong drink converted to be bitter; it is given "l'Marei Nafesh" (Mishlei 31:6).