Interesting idea. Your post raises Keats, of course, and the linkage of truth and beauty, though you distinguish b/w them. Recently I've been feeling art reveals certain truths in part b/c, almost paradoxically, it is in some ways removed from daily realities. Science strives for specific truths, and is continuously over-ruled or at very least updated. Same w/ history. But while art continues to change, it is not bettered. We will not see greater than Bach or Mozart or Shakespeare, only perhaps, if we're incredibly lucky, their equals or near-equals at some point. And in this sense, of something fairly universal and certainly lasting, there is indeed a quality of trueness.I've been thinking this about certain composers recently, and the emotional insight they give us. I find in these a kind of subtlety, depth, and psychological truth which would be hard to capture by other means. Prose moves linearly; one thing happens at a time. Music is able to express multiple dimensions simultaneously, much as life is experienced. Don Giovanni has a scene in particular where two meters are superimposed; Mozart's ensembles are famous for their complex layering. We can't reduce musical greatness to a single factor; in this sense, it more closely approximates reality's complexity than the traditional 'truth-telling' academic disciplines which are single-minded, logical, and linear in nature. More and more the science of the universe and of the brain supports this 'irrational' / enormously complex reality. Perhaps the greatest of our artistic creators understood this all along.
As much as music can raise one to sublime depths (if it's possible to be raised to depths, somewhat of an oxymoron), it is no more The Truth than anything else. Sublime feelings do not mean that one has reached at the Truth. If that were the case, then ecstatic religious feelings would also be seen as reaching The Truth.
If "truth" is different for each person depending on circumstances, then it is not a universal Truth. A truth that is not universal is merely a personal "truth", but certainly not "Truth".
