The Audio object doesn't support multiple tags yet, it's been on my todo list a while but hopefully will come some time. FYI the expression "music" & "title_loop" is identical to "musictitle_loop" after concatenation, so will definitely be treated as a single tag.
Whether or not audio loops seamlessly depends on the browser. I tried your example but I don't know how long I have to wait. AFAIK Chrome supports seamless loops, but Firefox and possibly other browsers don't yet.