Over the years I've used quite a few Macs and for whatever reason each time I've upgraded to a new computer I've started fresh with my iTunes library. On an external hard drive I have several previous iTunes libraries with songs not in my current, rather small iTunes music library. If I subscribe to iTunes Match, can I upload all the songs from each of these libraries so that they are unified under my Apple ID? This way I could download on-demand (which I see as essentially one step short of streaming) any of my songs on my current Mac, iPad, and iPhone without needing to fully merge my large former music libraries on my MacBook Air's minuscule SSD. After subscribing to iTunes Match, I would install a fresh copy of OS X on an external hard drive, boot up from it, and then use my Apple ID to upload the music from each of my iTunes libraries (by Option-clicking iTunes when launching it to select non-default iTunes library directories). I was just wondering if there was a guide or walk-through that explained the process or if anyone knew if this would work. Many thanks for the help!