Why did he say "Urah ha'Nevel v'Chinor"?
Rashi (57:9): Wake me, you lyre and harp suspended over my bed, open to the north. When midnight comes, the north wind begins to blow, and [they play, and] David rises and engages in Torah.
Radak: He metaphorically tells them to waken (or arouse) themselves [and play]. The prefix Hei in "ha'Nevel" calls to it, like "ha'Kahal Chukah Achas Lachem" (Bamidbar 15:15).
Malbim (57:9): The lyre and harp, which were silent until now, should arouse with pleasant songs.
Why did he say "A'ira Shachar"?
Rashi (from Bamidbar Rabah 15:16): Other kings sleep until three hours of the day. I wake [before] the morning (dawn); the morning does not wake me. Taz (OC 1:2) - it is an attribute to initiate arousal from below, and then there is arousal from above to reach a higher level 1 . David was at such a level that he did not need the arousal from above!
Radak #1: He tells the lyre and harp to awaken every morning, when he wakes them.
Radak #2: He tells the lyre and harp to arouse themselves when he arouses himself from his sleep in the morning to thank His name.
Malbim (57:9): Now the 'sun' of my success, which was dark until now, began shining. I.e. now Sha'ul himself recognized my honor, and said "Tzadik Atah Mimeni; ... Yadati Ki Maloch Timloch" (Shmuel I, 24:17, 20).
Yuma 39a: "V'Hiskadahtem vi'Hyisem Kedoshim" (Vayikra 20:7) - man sanctifies himself a little, from below, and [Shamayim] sanctifies him greatly, from above. Man sanctifies himself in this world, and [Shamayim] sanctifies him in the world to come.
