Okay, just to follow up on my last reply, I've been poking around here and there trying to find the answer to what I'm supposed to do, and did find one place that said to simply just insert the SVG images like one would insert any other image, basically. So I've tried that, and it does seem to work just fine in ADE -- if I re-size the window, the images stretch nicely and look good and everything -- but in iBooks on the iPad, although things seem okay at first when viewing it in two-page landscape mode, as soon as I rotate it to single-page portrait, the images don't stretch to the width of the page.
Like I said, I don't know what the heck I'm doing with these SVG images!
In fact, what's the reasoning behind using them in the first place? Why not just simply use JPEG or PNG images instead? I'd have no problem plopping those in and getting them to fit/re-size to the width of the page.
Anyway, here's an ebook I threw together with the sheet music in it, in SVG format, if you want to take a peek at how I did it (without knowing what I'm doing).