The truism that our postmodern ideas intrude into our interpretations of old music is well-known at this point, and barely needs repeating. Indeed, that it needed stating at all is somewhat distressing to me, but that is another topic. I'd like to encourage any musicologist who hasn't done so yet to read a historiography book or two at the first convenient moment. Anyway, it is time to take a look at this issue from a couple of different angles, because it is central to creativity for a traditional artist.
The necessity of finding our own ideas when we look for others is a problem for the museum curator, and the extent to which historical music can be an authentic recreation is severely limited by this constraint. Any time we do not know the answer, we are tempted to supply our own view. And why not? However, there is a difference between recognition of our limitations and basking in them. The latter so often leads to performance decisions which are one-dimensional or even insipid. It is a psychological challenge to begin with what we cannot do and proceed to create non-cynical art at the highest level, yet acknowledging limitations is often central.
So barring a totally new creation, one is left teetering on the uncomfortable edge between the abyss of nihilism and the glaring spotlight of self-assurance. That is the sort of tension which can be harnessed by the best performers. In a sense, the complexity of the issues surrounding an interpretation can yield a heightened sense of depth to the result, and this is just one reason not to leap for the easy answer. The extent to which we view our own self-involvement as a contaminant is also self-fulfilling, and indeed this applies analogously to the production medium. Hopefully this is the lesson of postmodernism, if in fact there is one.
The question is not whether a work should be changed for a modern audience, because with few exceptions it must be. Even the hypothetical museum piece is vastly different simply by virtue of its enforced static character. The bigger issue is how one builds an integral vision of such distant music, and ultimately how one allows the complexity of the situation to shine through in a natural way. The basic dynamic is forced to change as we exhaust the sources of older music upon which to draw. The possibility that we will have heard nearly everything of interest surviving from the medieval & Renaissance eras, mediated by virtually every written or iconographic source not only exists, but stares us squarely in the face. In fact, while it's possible there are a few more "great" works to be found, we undoubtedly know nearly all of them, if we are willing to assign such designations at all.
Such a thing may sound trivial, but it is certain to have a profound impact on the way early music interacts with the rest of our musical culture. Beyond a more personal identification with the music, something which simply requires sufficient exposure, "the way out" is clear and leads us back to the beginning. We will write new music using what we've learned, in effect expanding the musical canon. This will be done, but it is not an overnight process. For me, what makes traditional art so stimulating is that old & new are not in a reciprocal relationship, but rather in a dual one (we won't get into Abhinavagupta here, at least not today!). Literally, one modifies the other.
If we are determined to extract the masterpieces from this music and use them to supplement the Western canon as it stands, and I think we are, the supplement quickly dwarfs the core. It involves adding six centuries of music to the current two, and even if the former are less packed with goodies, they are no less broad in their stylistic range. On top of that, if we lump world traditions into some kind of massive classical fusion category, the scope of basic material is simply overwhelming. That, more than anything else, leads to the disparagement of this music by some classical music lovers. It is easier to do so, but it is a losing battle.
The first step in such a process is the continuous reevaluation of the core classical canon as new items are added by accretion. While it is important to keep in mind how the 19th century composers saw their own work, and what music they knew, we are able to place them in much sharper relief by looking back to the 13th century and beyond. This is a feedback process, and already has some impact on modern composers who might be basically unfamiliar with the work of e.g. Dufay. It certainly casts a different light on Schoenberg, because we not only perceive the harmonic cul-de-sac quite clearly, we see any number of paths around it. I suppose it is not surprising that Webern was known to have an interest in Obrecht & Ockeghem, and indeed that was my initial pointer to this music.
What we lack now is not ideas or inspiration, but rather focus. It is so easy to write something novel by combining world or Renaissance or electronic music with some of the core classical ideas that the process of creativity is in disarray. Or perhaps it is merely a critical synthesis which is lacking. Nonetheless, it is easy to see this focus emerging through familiarity, even if we are rather far away from producing the sort of resonant syntheses we might desire. I do not want to be too harsh on present attempts, because they are necessary and even laudable, but it is also important not to lose sight of loftier aspirations and the sort of intimate understanding & internalization which was necessary for the masterworks of the past. Perhaps I am overly optimistic or simply too mundane in my orientation, but I see the path as one of basic hard work at the personal level.