I will attempt to give a bit of an explanation:
There are different pesukim discussing from where our Neshama is sourced. The first is from בראשית ב, ו, concerning אדם הראשון, it says ויפח באפיו נשמת חיים. Meaning oppose to all of the other parts of creation, which comes from the speach of Hashem (עשרה מאמרות), our Neshama is coming from Hashem's breath (Metaphorically speaking of course), and the possuk uses the term breathing, to give us an understanding, (Since we can learn from people of how it exists above, being that Hashem created us in his image, as it says נעשה אדם כצלמינו כדמותינו) that just like our breath takes much more power, than when we just speak regularly, this is because our breath comes from a deep part within us. so too our souls, which is coming from the breath of Hashem is coming from a very deep part.
But how deep? That takes us to the next pessukim, where it mentions twice that we are sons of Hashem, once in שמות ד, כב saying בני בכורי ישראל. And a second time in ראה יד, א saying בנים אתם לה' אחריכם. Let's use us as the example again, being that a son comes originally from the thoughts of the father, that's the very first step. and the son is able to achieve and go way beyond a father's capabilities, shows us, that he's not just coming from the level of thought Which is revealed and is expressed by the father, but rather from a deeper part of the thought, the essence of thought, and then the son is able to express certain abilities, which the father couldn't. In this same way, being that we are Hashem's sons, We are coming from this same level of thought, from within Hashem - from the essence of Hashem's thought.
But still, this is just Hashem's thought... But since the rambam writes in יסודי התורה ב י, and in other places, that שהוא המדע והוא היודע. Meaning that by man there is 1) the person trying to understand, and 2) the subject he's trying to understand, it's two separate things. In contrast by Hashem it's all one, The knowledge and the knower, are all the same.
Therefore being that it's all one, if our Neshama is coming from the essence of the thought of Hashem. in reality, our Neshama is coming from the essence of Hashem. Hence, our Neshama is from the essence of Hashem or עצמות אין סוף.
This is only touching on the subject.
I`m sorry. You were good almost until the end, but last second managed to make conclusions that the baal hatanya himself would have never dreamed of uttering.
I`ll write a proper post after work, seems the biggest misunderstanding is people equating the lashon of chelek eloka mmaal and turning that into atzmus.
Even the baal hatanya says the neshama comes from machshava which is misacheid with hashem, as we know 'הוא וחכמתו אחד', היינו שהקב''ה הוא אחד עם ספירת החכמה שלו.
But just stop saying Atzmus you guys are talking kfira in the highest degree without even knowing it, the sources you quoting are NOT saying what you saying. PERIOD.
We know that קוב''ה ואורייתא חד would you now conclude that the torah created the world as well?
Heres what the ramban al hotorah says about the neshama which the Tanya obviously doesnt disagree with.
וז''ל עה''פ ויפח באפיו נשמת חיים [בראשית ב, ז] ירמוז לנו הכתוב הזה מעלת הנפש יסודה וסודה כי הזכיר בה שם מלא ואמר כי הוא נפח בְּאַפָּיו נִשְׁמַת חַיִּים להודיע כי לא באה בו מן היסודות כאשר רמז בנֶפֶשׁ התנועה (לעיל א כ) גם לא בהשתלשלות מן השכלים הנבדלים אבל היא רוח השם הגדול מפיו דעת ותבונה כי הנופח באפי אחר מנשמתו יתן בו וזהו שנאמר (איוב לב ח) וְנִשְׁמַת שַׁדַּי תְּבִינֵם כי היא מיסוד הבינה בדרך אמת ואמונה והוא מאמרם בספרי (ריש פרשת מטות) נדרים כנשבע בחיי המלך שבועות כנשבע במלך עצמו אף על פי שאין ראיה לדבר זכר לדבר חַי ה' וְחֵי נַפְשְׁךָ וגומר (מלכים ב ד ל), עכל''ק.
I will talk to some knowledgeable Chabad people I have no safek that will not in a billion years dare say what you guys are saying.