Hey,
I have little experience in modding, and have had my share of problems with Skyrim's CK so far, but I have managed to piece together the processes for a few things from the numerous and confusing online posts/websites.
I figured out how to add my own music or scores for specific moments. So far I have only added 6 or so scores for when you enter combat (the same monotonous single battle tune was wearing a bit thin).
1. Download a file converter so that you can convert your mp3's etc etc to ".wav" files, I used this one and it seems to work ok, although it's a bit buggy I think, there are probably better quality ones out there.
http://apps.foxtab.com/musicconverter/
2. Go to the Skyrim "Data" directory on your computer and make a new folder called "music". For me it was: C:\Adam's\Games\Skyrim\SteamApps\common\skyrim\Data\music...
Put the newly converted .wav files in the new "music" folder you made here.
3. In the Creation Kit, within the "Object Window" go to Audio > Music Track > MUSCombat01. Duplicate this file, or simply change its properties directly (up to you, I changed its properties since I wanted to not only add music but remove the existing tunes as well). I removed the "cue points" since I didn't want my new music to cut in and out before the song was completely finished, and then I clicked on "Choose File" (which was blank) and searched the new "music" folder I made and selected the single song I wanted to replace the crappy tune with. I simply left the "Choose Finale`box as is; and of course if you want you can change the other options, like the conditions under which the music will activate (I just left all that for now and every time I enter combat, whether vs a dragon, humanoid, or creature my new tracks kick in).
4. Under Audio > Music Type go to "MUSCombat" and right-click on an entry to either delete it or add a new entry referencing one of the new tracks you just added through step 3 above.
Hopefully this helps, it's worked for me and so far I haven't had any issues.