|Christ giving the Keys to St Peter: Pietro Perugino (1481-1482) Sistine Chapel|
> but I'm afraid I can't conclude God's voice is that of the Magisterium at least on some issues.
That's an epistemological problem between Catholicism and gnosticism/ nihilism.
It's pretty binary: Either A) Christ founded the Church as a sure and objective means of knowing the Gospel, and endowed the Church with the gifts to safeguard the teaching in matters of faith and moral so that we can be certain of how we must act and what we must hold and believe in order to conform our lives to God's plan and purposes for human relations; or B) there is no sure way of knowing anything about faith or morals, only objective material facts.
If B, then all interpretation is just a subjective gnosticism -- my own experiential knowledge (gnosis) is all that counts and by that I judge the Church as deficient.
I don't see a third way here -- either the Church is what she claims to be, along with her mission, sacraments, teachings in matters of faith and morals, and essential structure -- or everything is up for grabs. At that point the Church is nothing more than a social club of like minded people who like the Church for whatever comforts one subjectively finds in that association. There can be no mechanism where we can know that any one point of doctrine or any one act of the Church or any one moral teaching has anything to do with God's plan and purpose, with his will for our lives together or as individuals. So all valuation is likewise subjectively determined (not even "culturally constructed") and there is no reason to objectively value one thing over another.
It's basically why I am Catholic rather than a nihilist or a gnostic. Picking and choosing what parts of the Magisterium to attend to is not the practice of the Catholic faith but one's own personal and private religion where the Church is only true as long as it reflects what you demand of it.