Some make the argument that because echad is used in passages such as Gen. 1:5 (evening and morning were "day one [echad]", or "first day"), Gen. 2:24 (a husband and wife shall be "one" flesh) and Ezek. 37:17 (two sticks are to become "one" stick), echad is therefore meant to be understood as some kind of a compound unity. To begin with, such examples make up but a very small minority of the uses of echad, the vast majority being of the variety listed above. It is improper exegesis to define a word on the basis of a small percentage of its usage. But even this extreme minority of usage does not mean that echad actually has a different meaning than a simply one in these passages. In Gen. 1:5, "day" is the word that has "parts" to it (i.e., "evening" and "morning" make up the day), not echad. In Gen. 2:24, "flesh" acts as the collective noun (what the man and the woman as comprise together). [12] The key factor in all such passages - a factor missing from Deut. 6:4 - is that two or more "parts" are mentioned, such that the reader can immediately discern that there is some kind of "coming together" of the people or things mentioned, usually for just one purpose or goal. Echad, in fact, must maintain its meaning of "just one" for these expressions to convey their intended sense. To make our point clear: Deut. 6:4 does not say, "YHWH our God, though three (or two or whatever plural number you like), is one." There is no hint of "coming together" here. The verse says that YHWH our God is plainly, simply, one.
Wooaahh there, Nelly. You just got tripped up in your own words. The key factor is the word "Elohim" which the link admits is a plural form which would be that key factor for the word "echad" to then mean a "compound unity".
Thus the SHAMA of Deuteronomy 6:4 can most definitely teach a compound unity regarding Elohim, especially when compared to the use of the word "ONE" regarding Jesus and his Father in the New Testament, whose relationship would be the model for the compound unity of the apostles: "that they might be ONE even as we are". There were [was] more than one apostle, weren't [wasn't] there?