Thanks for the additional info.
As for ambient music, when I was in graduate school I always had classical music in the background. I was fortunate - it was WFMT (35 years later and I still remember its call signal) which was generally commercial free or limited. I also had my reel-to-reel which had hours of music or "reel" commercial-free music. Over the years I've grown out of the habit and having a partner who could not abide by any sound while she read - well, music disappeared.
I've not really used the mp3's I loaded on the kindle - probably because you cannot control their play order. I may revisit your site and see what "transparent" tunes you've created.