An interesting point; the problem being that Issiah (7 and 8) does not speak of Immanuel as a messiah but rather prophesies that the birth of this child is a sign given by god that would demonstrate that
Assyria would not destroy Judah yet invade Syria and Ephraim (circa 730BCE) Mathew attempts to suggest that Jesus is the fulfillment of this prophecy (
RF Thread on this topic) in order to suggest immaculate conception (a different thread) and to somehow claim for Jesus the name Immanuel (which he was never addressed nor is there any indication that was a name ever used with reference to him during his life time). However the Immanuel in Isiah was not a messiah but a symbol of god's providence in showing that Judah would be safe, but even if you suggested he was a messiah, there is nothing to indicate that this particular messiah would be special compared to others. There are many names in the bible that include 'god' the most striking being 'Israel' (God Rules); Immanuel 'god is with us' is merely a reflection of god being with the people of Judah and that therefore they would be safe from the assyrians. IMO the link to Isiah's Immanuel prophecy is the least compelling prophecy for jesus's messianic nature; the Star and Scepter prophecy is far more interesting.
Though TBH your attempt to identify OT prophesies at the moment to support your claim sort of undermines your earlier arguments that the OT and NT arent really supposed to reconcile.
Assuming the position they are not supposed to reconcile, there is no need to look for OT prophesies: to paraphrase one of your earlier arguments you can know he is god because he performed miracles and people at the time thought he was god, therefore he was god.
To maintain consistent with the assertion that the OT and NT are not supposed to reconcile, there is no need to look at the OT at all for any suggestion of Jesus' divine nature, or indeed for many other reasons, though this later is somewhat undermined by Jesus himself pointing out that the OT was to be obeyed. So the OT remains relevant, even if as you suggest the two are not meant to reconcile; just how you square the two characteristics (non-reconciling yet relevant) in such a case is up to you (but regardless, there would be no need for OT prophesies if the two are not meant to reconcile because you are asserting a completely different means of authenticating his divine nature than OT prophesy).