Balancing the soundtrack or white balancing isn’t going to get you anywhere, as the sensor response is far more complex than a simple RGB curves adjustment will allow you to correct. Then there’s the bigger problem, that color perception can differ quite substantially from person to person:
http://www.livescience.com/21275-color-red-blue-scientists.html
So, adjusting colors watching a projected print may seem like a good idea, but in many ways the way our eyes and brains sense and interpret colors is quite similar to how a scanner sensor works. You might adjust the colors to roughly match what you personally are seeing, but someone else may sense and interpret these colors differently. Taking a number of different people and having them adjust colors by eye watching a screen, will almost certainly yield quite a variation of results, similar to taking a number of different scanners and comparing the responses of the scanner sensor. Now matching the tones you see on a calibrated screen to a projection will bring the colors closer to what they should be, even if we percieve them differently from each other. However, the accuracy will depend heavily on the sensitivity of our eyes to different tones, which in of itself depends heavily on hue, luminosity, and saturation.
Now, the scanner detects the light after it has passed through the dyes and film. This light has a specific distribution of wave lengths, depending on the combination of dyes and film, and thus determine it’s color. While it is true, that a different film stock will alter the colors, this should not affect the color calibration, which is simply mapping the colors detected by the sensor after passing through the dyes and film onto a reference file, which was also calibrated based on a combination of dye and film. The important point here is, that it is the color of the light detected by the sensor, which is calibrated, not the color of the dyes themselves. While the color gamut for a piece of Technicolor film will be different from the color gamut of the it-8 target, they will overlap to a large degree. In other words there usually exists a unique combination of Technicolor dyes and film, which transmits the same color light as a color patch on the it-8 target, even if the dyes and film are different for the it-8 target. The inaccuracies introduced at this point are caused by the precision of the sensor, and reflectance of the film material, which is generally very small compared to the transmitted light captured by the sensor.
I might actually agree the darkest and brightest colors may be skewed somewhat for these scans, since the it-8 color target is geared mostly towards correcting the mid-tones. However, I do think the mid-tones should be accurate. Therefore, I still believe using a generic it-8 color calibration target is the next to most objective and accurate way (assuming you don’t have a film specific color target) to ensure hue representation is accurate over a large range of tones, even if contrast and saturation will heavily influence how each of us percieve these hues when contrast and saturation is adjusted.