This which you have posted, has either flown over my head, or around it. I will need to study this more in depth before I can give what I would believe to be an adequate response.
Now, onto something I'd like to present:
Hebrews 8
1 Now of the things which we have spoken this is the sum: We have such an high priest, who is set on the right hand of the throne of the Majesty in the heavens;
2 A minister of the sanctuary, and of the true tabernacle, which the Lord pitched, and not man.
Hebrews 12
1 Wherefore seeing we also are compassed about with so great a cloud of witnesses, let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us,
2 Looking unto Jesus the author and finisher of our faith; who for the joy that was set before him endured the cross, despising the shame, and is set down at the right hand of the throne of God.
Jesus is sitting on the Throne now, on the right hand of His Father. He has already usurped David and taken his place.
1 Timothy 2
1 I exhort therefore, that, first of all, supplications, prayers, intercessions, and giving of thanks, be made for all men;
2 For kings, and for all that are in authority; that we may lead a quiet and peaceable life in all godliness and honesty.
3 For this is good and acceptable in the sight of God our Saviour;
4 Who will have all men to be saved, and to come unto the knowledge of the truth.
5 For there is one God, and one mediator between God and men, the man Christ Jesus;
6 Who gave himself a ransom for all, to be testified in due time.
Jesus, being on the right hand of the Father in heaven, sitting on His throne, is our mediator, our advocate, our big Brother, our intercessor. This is why I believe He is on the throne of David now.
You need to study this after you study the other.
Acts 2:34,35 For David is not ascended into the heavens: but he saith himself, The LORD said unto my Lord, Sit thou on my right hand, Until I make thy foes thy footstool.
David is both dead (his soul is presently left in Hades) and buried (that is his flesh saw corruption) He, (David) is not in heaven, The Lord (God the Father Of Jesus the Son) said unto my (David's) Lord (Jesus the son also the Son of Man that is of David) sit thou (Jesus) on my (God the Father's) right hand until I (God the Father) make thy (Jesus the Son) foes thy (Jesus the Son's) footstool.
Then the kingdom of God, the throne (tabernacle, house) of David will be established at his appearing.
As OR asked in next post, how did this throne get to heaven?