How does the concept of "Echad" in Deut 6:4 relate to Divine Simplicity?

Lately I've read some discussions that says the word "echad" ("one" in English) in the Shema refers to a unity more than an absolute singularity. (Here's one example of those explanations) and would then compare it to husbands and wifes becoming one flesh, among other things. Some even would use the terms "absolute unity" in comparison to "compound unity" These are done, based on my understanding, to support the Trinity via the Old Testament. >Hear, O Israel: The LORD our God is **one LORD**: And thou shalt love the LORD thy God with all thine heart, and with all thy soul, and with all thy might. [Deuteronomy 6: 4 and 5 KJV] However, in light of what we know of Divine Simplicity, this doesn't quite make much sense to me, and would seem contradicting: God is not a union of separate individuals (like the husband or wife is, or a nation, etc), nor can He be said to be "compound" because He is not composed of parts. With these in mind, I wonder how the concepts of Divine Simplicity and Echad as "compound unity" relate to each other - can they be reconciled at all? Or should Deut 6:4 be even used to support the Trinity in the first place? What do I miss?