Ok, so the thing is, for your case scenario, you definitely need to use (try) emby, because the official mysql support is just for local lan, more so, it enables you to use the same database across various devices, however, that works only for one user, if its more than one user (still local lan only), theres some workarrounds to using a modified mysql db to make it simple for multiple users, multiple devices, which is what I am/was using, however, it hasn't been updated to kodi 15.
The solution, emby, basically let's you do what mysql does with some advantages, similar to what plex offers, like internet streaming. The only caveat is that in my case, it means a computer running 24/7 besides my nas. In my case is going to be a small netbook which I had laying arround that appears to work fine for emby and a few other stuff. Do keep in mind that altough emby is able to run just fine on low powered computers, if you need transcoding capabilities (recommended when online streaming), you need a beefier pc.
So I think you should give emby a chance, is very easy to setup, even more on windows. If you decide to try it and need any help, send me a pm so not to go off topic anymore here.
The only concern I have is will the 320L cope with 2 or 3 users streaming at the same time?
A: Well, that depends on a couple of things, the most important are bitrate of your videos, speed of your local lan (gigabit or just 100mb), and your internet up speed.
For local lan, if you are running gigabit ethernet, I think 3 or even 4 users should be more than fine on compressed video (ie not ful bluray rip). The internet side of things I couldn't tell you because I don't do that, plus my internet up speed sucks.