HTML5 audio libraries

You may have already selected a library, but as the developer of howler.js, I thought I'd leave a note. From your description, I'd say howler.js is exactly what you are looking for if you don't need less than IE9 support. howler.js has now been under development/refinement for nearly a year and has a large community around it. It is great for both simple and complex tasks, and leaves any UI needs up to the developer. howler.js is currently the only library that I'm aware of that lets you seamlessly use both Web Audio API and HTML5 Audio with a single, simple API.

My recommendation would be SoundJS, but I may be biased because I work on it.

It allows you to get audio up and running with minimal code that will work across all modern browsers. Looping and playing from an offset both work smoothly. As far as I know, looping only a slice of a larger audio file smoothly can only be done with pure web audio, which currently is only supported in Chrome and Safari. SoundJS doesn't support that functionality directly, but does allow you access the web audio nodes directly so you can set it up manually.

Hope that helps.