It's as Alx330 has mentioned, BubbleUPnP Server is not a media sever (note it is not called BubbleUPnP 'media' server). You are probably confusing it with the well known Android app, BubbleUPnP, which can run a UPnP/DLNA media server on the Android device it's installed on, as well as providing a UPnP/DLNA controller/control point and a local UPnP/DLNA client/player.
BubbleUPnP Server is mainly used to provide UPnP/DLNA access to your own media servers over the internet and can also be used to fix existing problems between your UPnP/DLNA servers and their clients. The actual definition of it is (from http://www.bubblesoftapps.com/bubbleupnpserver/
BubbleUPnP Server provides new services on top of your existing UPnP/DLNA devices:
secure Internet access to your UPnP/DLNA Media Servers content with BubbleUPnP for Android and foobar2000 on Windows (or Wine).
stream and download your music, video, photos with your Android device from a mobile or WiFi connection with optional transcoding to reduce bandwidth.
no need to sync, to upload to the cloud, to register to an online service, ... You're in control!
create OpenHome Media Renderers from any UPnP AV renderer (provides on-device playlist, multiple Control Point access to the same renderer). Works with BubbleUPnP for Android.
fix issues of UPnP/DLNA Media Servers (discovery issues, broken data, add some audio DLNA compliance) by creating a proxy Media Server
BUBBLEUPNP SERVER IS NOT AN UPNP AV MEDIA SERVER
It requires at least one working UPnP AV Media Server (Windows Media Player, Twonky, Asset UPnP, ...) or Media Renderer to do something useful.
You probably won't need BubbleUPnP Server, unless you are planning on accessing your own media servers from the internet. I don't believe it works well (if at all) with any of the Microsoft supplied media servers that might already be running on your pc, such as that from Windows media player. WMP/WMS is not considered to be a good media server to use for music, because of its lack of support for many music file types as well as not being very configurable.
In addition to the UPnP/DLNA media servers mentioned above that you can install on your pc, other specialised music only free media servers I would recommend are: Minimserver and Foobar2000 with the foo_UPnP plugin. You can run more than one media server on your pc at the same time, so that you can compare them to see which one is best for you (ease of use, facilities, etc).