One has to understand the implications of the words Aham (ME) and Tvam (You) when used in the Indian Philosophy when it applies to Spiritual Liberation, which is the final aim of Yoga.
The word Tvam is used to denote God, Brahman, or even personal deity. Whereas, the word Aham is used to denote individual, Soul, or even a devotee of a deity.
e.g. the word Tvam in Tat Tvam Asi (That Thou Are) definitely means Brahman, the final reality behind the entire existence. However for a devotee, his/her own deity denotes everything including Brahman. The concept of Deity permits the Devotee to interact with the Almighty.
e.g. the word Aham in Aham Brahmaasmi (I am the Brahman) obviously means Brahman. A devotee does not like to say this way as devotee wants to enjoy the act of devotion. However, as the devotee becomes totally engrossed in the devotion, he/she perceives the unity with the deity and even at times behaves like a deity.
When a worshipper prays for material benefits he may call the deity with Tvam and praise the deity as You are the Fire, You are the Speech, etc. and also you are the Brahman itself.
When the yoga student rises the heights of non-duality, he/she realizes the unity with the Brahman and may use the word Aham.
Thus, Aham and Tvam are synonymous in effect, even if they mean opposite in the dictionary meaning!