About Jack, let me repeat this one more time Jack is not necessary at all to obtain low latency, ALSA is more than enough; if you're writing audio software, having Jack support is nice, but please don't depend on it as it just complicates things.

I mean, technically JACK is built on top of ALSA, you can always get lower latency by going through ALSA directly than by involving JACK... but it's pretty hard to implement correctly.