As-salam aleikum wa rahmatullahi wa baraketuh,

dear brother Ramihs97, it is a long subject to discuss here all of the details, so I will try to explain it you briefly:

1. In regards to the word etmak in DSS (Isaiah 42:1), there are strong cases which indicates that it is an altered form of ahmad. Kab al-Ahbar (d. 652), a learned rabbi from Yemen was quoted by Ibn Asakir as saying:

I find in the Torah: Ahmad, My Chosen Servant (in another narration: My Servant Ahmad, The Chosen). Verily, he is neither rude nor harsh. He would not yell or scream in markets. And he will never award an ill deed with an ill deed, rather, he will always award ill deeds with forgiveness.

Notice that he was quoting Isaiah 42:1-3. In LXX the name Jacob appears first, and then "My servant" so it refers to the first variant narration mentioned by Kab i.e. "Ahmad, My servant". In Masoretic Text, the chapter begins with [Behold] My servant, and then etmak, so it refers to the second variant narration mentioned by Kab, i.e. My servant Ahmad…. Now, the fact that Kab mentioned two different variant of the first fragments from Isaiah 42:1 indicates that there were different manuscripts containing different variants of reading, as I've said above in the case of Septuagint and Hebrew text we have today. In LXX, the Jews must have inserted the words Jacob and Israel instead of Ahmad, since it does not appear neither in Masoretic Text, neither in Aramaic Peshitta, nor in 1QIsaa. There are too possible way to explain the origin of etmak:

a) NON-INTENTIONAL CHANGE - The Jewish scribe could have misread the original form אחמד (ahmad), because in general, the Hebrew letter ת(tav) is visually very similar to ח (chet), and the letter ך (kaph) looks very similar to ד (dalet). The later one i.e. kaph and dalet are especially similar to each other in the old Aramaic alphabet. 
b) INTENTIONAL CHANGE - The Jews could have changed the name of Ahmad when they acknowledged that Prophet Mohammed is an Arab not Israeli (6th century AD). In fact there Ibn Saad in his Kitab Tabaqat al-Kabit related a narration from which can be concluded that immediately after their acknowledgement of prophet's Mohammed Arabic roots, Jews deliberately changed the name Ahmad. It says that this Jew changed Ahmad by covering or hiding it not removing it entirely. The natural consequence of such argumentation is that till Prophet's Mohammed time there were no attempts to corrupt his second prophetic name Ahmad, so the pre-Islamic Torah would have not made any modification. You will ask: but what about DSS ? The Great Isaiah Scroll does not mentioned Ahmad, but etmak right ? You should know that before DSS were discovered, the earliest manuscript of the Hebrew Bible were Aleppo Codex and Leningrad Codex (10th century AD). So it was easy for Muslim to claim: Mohammed was mentioned in the original Torah (i.e. from ancient times), but you Jews do not possess such one, you have only those one dated back to 10th cent. so how we would know whether your rabbis does not changed the Torah after the time of Mohammed ? So what was the plan ? They must prepare some kind of proto-Masoretic Text which would agree their Masoretic one from 10th cent. (but in order to eliminate a possible suspicions from intelektualists they gave a multiple variations of textual reading so to keep scholars constantly working on formulating new theories, resolving puzzles etc.). Can you believe in this fairy, stupid story about a Hebrew text from 2 cent. BC which perfectly agrees in chronological order of chapters and verses, and with no significant departure from its Masoretic version ? I will never believe in such a crap. There was different arrangement of whole chapters in Isaiah. Frankly, there are serious reasons to think that this so called Great Isaiah Scroll which has been claimed to come allegedly from 2 cent. BC. is not an ancient autograph (at least in part). This Isaiah Scroll in many passages shares the same textual variant as the Hebrew MSS from medieval period collected by Kennicott and de Rossi.

Let us return to the subject of mentioning Ahmed in DSS. 

If you recall Matthew 12:18 you will see that his quotation is unique, i.e. is not similar as in Old Testament Hebrew Isaiah or Greek Septuagint:

Behold, my servant whom I have chosen, my beloved (agapetos) with whom my soul is well pleased. I will put my Spirit upon him, and he will proclaim justice to the Gentiles.

According to early church tradition, the Gospel of Matthew was originally written in Hebrew, and then it was translated into Greek. Notice that in Matthew you will not find such word as whom I uphold/I support for Hebrew etmak. Why ? Here is the answer… the Greek term ἀγαπητός (agapetos) for my beloved which occurs in the text of Matthew 12:18 is actually an equivalent for Hebrew חמד (chamad) found e.g. in Joshua 7:21 under the form אחמדם which can be read as ahmadam or echmedem. The point I 'am going to is that the Hebrew scroll from which Matthew quoted Isaiah 42:1 must have contain the word composed with the root חמד (chamad), yet it cannot be found in today's Masoretic Text ! Beside this, there are many other details which supports the view that the name Ahmad indeed was mentioned in the original text of Isaiah 42:1. 

2. In regards to the Zohar book, it is a great possibility that it talks ocasionally about Ahmed, notice the words occurring around it: through him in ancient of days, Isaiah, sent etc. I 'am simply guessing that it is about prophet Ahmad who was foretold in Isaiah and from ancient of days. I currently waiting for the answer of some certain rabbi. The text of Zohar is specifically in Aramaic, not in Hebrew as I previously thought.

Take care, and salam
Ahmed (Poland, Warsaw)