I've been playing with SpectraLayers Pro for the last few weeks, and I have to say that this, ladies and gentlemen, is what we've all been waiting for.
After only learning the most basic functions of it and just kind of messing around with the options it offers, I'm already seeing some really impressive results on my attempts at removing the music from Star Wars: A New Hope -- which, let's face it, is the number one film from which we fan-editing types would like to erase the music. I can only imagine how good the results might be in the hands of someone with more time (and, ideally, more technical expertise) to devote to such a thing; this program is very, very good at removing music (and sound effects, and dialogue).
There is a learning curve, of course -- it's pretty trial-and-error at first, because you're sort of blindly figuring out what is and is not music/dialogue/sound effects/etc., but one quickly learns what to look for in the waveforms, and from there it's a matter of figuring out the best approach, tool-wise, for removal of a given sound -- and there are numerous options.
I should say now that this isn't a "magic wand" situation, nor is it the sort of thing where you select a setting or two and the job is done. This isn't a matter of a simple phase inversion to the audio's center channel or something; it's more akin to cleaning up a picture in Photoshop: one must zoom in and identify problems on a case-by-case basis and then fix them using a fairly wide selection of combinations of tools and settings.
I think in order to truly and successfully clean up A New Hope, it'll take weeks or even months of meticulous, granular work. That said, I really do believe that it's 100% possible now to remove the music completely if one is dedicated and serious enough about the endeavor.
The whole process is subtractive, of course -- you can't erase audio from a recording and leave the rest of it untouched -- but if one were to be properly selective about what stays and what goes, and perhaps if they're aided by inserting bits and pieces of already available "clean" audio clips, I think the results could be more or less indistinguishable from a genuine copy of the film with no score.
Simply put, SpectraLayers can remove what you don't want, but leave what you do want.
Gentlemen, start your engines.