I found it simple to add own music tracks to Soundsense, thanks to its great design. Here's my example, I added two tracks called campaign_summer1 and campaign_summer2
If you add lines to System-folder, it might play the track when it loads the fortress/reclaim or whatever is the option, right? As developer mentioned, Soundsense plays a random track at beginning...
<sound logPattern="\*\* Loading Fortress \*\*" channel="music" loop="start">
<soundFile fileName="../seasons/spring1.mp3" />
<soundFile fileName="../seasons/spring2.mp3" />
etc
<soundFile fileName="../seasons/summer1.mp3" />
<soundFile fileName="../seasons/summer2.mp3" />
<soundFile fileName="campaign_summer2.mp3" />
<soundFile fileName="campaign_summer3.mp3" />
<soundFile fileName="../seasons/autumn1.mp3" />
<soundFile fileName="../seasons/autumn2.mp3" />
And adding new lines to Seasons-folder, it plays my tracks according to season. Simple.
<sound logPattern="(Spring has arrived!)|(Spring has arrived on the calendar\.)" loop="start" channel="music">
<soundFile fileName="spring1.mp3" />
<soundFile fileName="spring2.mp3" />
<soundFile fileName="spring3.mp3" />
<soundFile fileName="spring4.mp3" />
</sound>
<sound logPattern="(It is now summer\.)|(Summer has arrived on the calendar\.)" loop="start" channel="music">
<soundFile fileName="summer1.mp3" />
<soundFile fileName="summer2.mp3" />
<soundFile fileName="campaign_summer3.mp3" />
<soundFile fileName="campaign_summer2.mp3" />
</sound>
<sound logPattern="(Autumn has come\.)|(Autumn has arrived on the calendar\.)" loop="start" channel="music">
<soundFile fileName="autumn1.mp3" />
<soundFile fileName="autumn2.mp3" />
<soundFile fileName="autumn3.mp3" />
</sound>
<sound logPattern="(Winter is upon you\.)|(Winter has arrived on the calendar\.)" loop="start" channel="music">
<soundFile fileName="winter1.mp3" />
<soundFile fileName="winter2.mp3" />
<soundFile fileName="winter3.mp3" />
</sound>
I also added new music (tracks mobilise3 and mob4) for beasts/sieges/ambushes:
As mentioned, tracks need to be in same folder what XML you're editing: in my case, Intruders and Seasons.