(1) Otto Kaiser (OTL) professes that the King (or Messiah) mentioned in Isa. 9:6 is EL GIBBOHR insofar as he is "the representative and viceregent of God on earth, who, as the one endowed with this spirit (cf. 11:1), shares in his nature and his will" (Isaiah 1-12, Page 213).
When Kaiser claims that the Messiah-King shares in "the nature" and "will" of God, his statement should not be construed to mean that he believes the King shares the essence of God (i.e., the divine attributes). To the contrary, the King that Kaiser provides commentary about is fully human. This point is clearly brought out when Kaiser explains that the words "Wonderful Counselor" characterize: "the ruler as a man who, like God, can make extraordinary resolves and then carry them out. Illuminated by Yahweh himself, he needs no counsel from others . . . The second name [Mighty God] stresses his abundance of power, calling men to their God" (213).
Kaiser also contends that Isa. 9:6 possibly shows hints of Egyptian influence on the royal ritual of Israel (a point some have insisted applies to Ps. 45 and Heb. 1). For an interesting discussion of this matter vis-a'-vis Revelation 5:1ff and the coronation of the Lamb, see David Aune's thorough notes in his Word commentary (Revelation 1-5). But whether Isa. 9:6 shows Egyptian influence or not, Kaiser demonstrates by means of parallels why Isa. 9:6 is not necessarily proof for the Deity of Jesus (even though it is clearly Messianic). Please see the Catholic NAB and its handling of this OT passage since the NABRE appears to have changed the footnote found in the older NAB.
(2) Isa. 9:7 indicates that the Messiah would rule by the power of YHWH. A similar point is made at Mic. 5:4, where the Messiah is said to rule in the strength of YHWH. There is abundant proof that Mic. 5:1-4 is what we would today call--a subordinationist delineation of the Messiah.
For Kaiser's commentary, see https://books.google.com/books?id=15a7BwAAQBAJ&printsec=frontcover&dq=isaiah+1-12+kaiser&hl=en&sa=X&ved=0ahUKEwjf6669vsvNAhUF5iYKHSkLD1MQ6AEIHDAA#v=onepage&q=isaiah%201-12%20kaiser&f=false