For a Child hath been born to us, A Son hath been given to us, And the princely power is on his shoulder, And He doth call his name Wonderful, Counsellor, Mighty God [Hebrew transliteration: EL GIBBOR], Father of Eternity, Prince of Peace. -- Isaiah 9:6, Young's Literal Translation.
As given in Young's translation, it shows that the titles are anarthrous, without the definite article "the" before each title. Of course, the capitalization of these "titles" are also added be the translators.
What does the trinitarian need to assume concerning Isaiah 9:6? First, it appears that he would assume that "name" (singular) really means "names" (plural) or titles (plural). Then he has to assume that EL GIBBOR is a singular name/title applied to Jesus. Then he has to assume that EL GIBBOR, as applied to Jesus, means that Jesus is Yahweh.
It is Yahweh, however, who is giving the son to Israel, and it is also Yahweh who is giving this "name" to the son, as can be seen in Isaiah 9:7, "The zeal of Yahweh of Hosts will perform this."
If EL GIBBOR should be understood as being a title of Jesus in this verse, the context should let us know that the expression "el gibbor" would not signify Yahweh. Therefore, we should determine the meaning el gibbor as it would apply to the one given by Yahweh, and not automatically assume that it means that Jesus is Yahweh. In keeping with the context, then it should be understood as the term is used in Ezekiel 32:21, where the same expression in the plural is used. I do not know of any translation that renders the expression in Ezekiel 32:21 as "Mighty Gods", but it is usually rendered similar to the King James Version, which renders it as "The strong among the mighty." Thus, in Isaiah 9:6, if this expression as "mighty god" is assumed to be a title for the Messiah, the anointed of Yahweh, who is therefore not Yahweh, then it should also be understood as in Ezekiel 32:21, "a strong one among the mighty."
Likewise, if the title "everlasting father," is to be understood as being applied to the Messiah, it should be understood in light of what Messiah became after his resurrection, the "last Adam," who "became the life-giving spirit," who, in effect, is takes Adam's place as the life-giver to the world. Unlike Adam, who disobeyed and became father only to a dying race (1 Corinthians 15:21,22), Jesus becomes father forever, thus "everlasting father."
However, the prophecy of Isaiah 9:6 depicts a singular name by which the son who is given shall be called. The name given is given by Yahweh. The name, being singular, does not depict a series of names or titles as is given by most translations of this verse. That singular name is usually transliterated as Pelejoezelgibborabiaadarshalom. Often such a "name" given to a human or a thing is describing attributes of God/Yahweh, and the application of such a name to a human or thing does not designate the human or thing as being God/Yahweh. Thus, for instance, when Jacob called a certain altar by the name, El-Elohe-Israel, which could be read as a series of titles: God, The God, Israel, we realize that this is not what Jacob meant by this. Rather, we understand that he was not saying that the altar was "God," or that the altar was "the God," nor that the altar was Israel, but rather that the name of the altar was meant to say something about Jacob's (Israel's) God. Thus, this name is usually given a meaning something like: "God is the God of Israel," or probably more likely, the first EL should be understood with the general meaning of might, strength, power, etc., thus: "Powerful is the God of Israel." Likewise in Isaiah 9:6, since it is directly stated in the singular as a name, not plural, as "names", we believe it more correctly to be understood as describing Yahweh, not the Messiah who comes in the name of Yahweh. Some editions of the JPS give this name the following meaning: "Wonderful in counsel is God the Mighty, the everlasting Father, the Ruler of peace." From this perspective, this singular name that is given to Messiah would be describing the God and Father of Messiah, not the Messiah himself.
Nevertheless, as shown above, even if Isaiah 9:6 should be viewed as a series of titles describing the Messiah himself, it still does not mean that Jesus is Yahweh who sent Jesus. There is definitely nothing in the verse about three persons in one God or any kind of concept as expressed in the trinity dogma, except that one add that dogma to, and read that dogma into, what is stated in Isaiah 9:6.