Gino,
First, let me start by saying that in Greek, there was no such thing as capitalizing headings and or names. In fact at the time of the writing of Hebrews there were ONLY capital letters, and no punctuation and or spaces for that matter.  So when You talk of the difference between the king of Salem and the King of Salem, you are reading a distinction there, where none could possibly have ever existed.
 
I Know you are KJV only, but the ESV got that one right. All the commas, periods, exclamation points, etc. were never in the original text, and to rely on them is to lean on man for understanding.
 
Regarding the point of your topic, We as Christians see Melchizedek as a Christophany, and Hebrews 7 seems quite clear on this saying the following: " He is without father or mother or genealogy, having neither beginning of days nor end of life, but resembling the Son of God he continues a priest forever. (3:3)
 
I Briefly wrote on what I think you may be seeing here. There are three 2000 year Ages, the first age was that of the Father. (The Hebrew people call this the Age of the fathers) and you are touching on the fact that the concept of "Son" was yet to be revealed to the Israelites. You Have to Remember that Jesus Was, and IS an IS to come. He never had to ascend to the position of High Priest, He always was High Priest. When He came to earth in Human form, He humbled himself (Phillipians 2)
 
But to say you are in error in saying that this was a theophany is kind of misleading as Theophany and Christophany are one in the same as God is ONE. With regard to The ONENESS people, What they fail to take into account is the perspective of the viewer. So In this case, Melchizedek of The OT may appear as a theophany, But from our perspective we see it as a Christophany because the Son has been fully revealed to the early church. It is that third person that has yet to have that full revelation that we should be concentrating on. I am going to create a new word here, so bear with me... A Holy PNEUMAPHONY.  That is when God within Us is revealed. I Cannot not explain this, nor defend it, but I know it will occur soon!
 
God Bless.