Hmm... I'm not sure if this will work or not, but you can try this:
1) In a Finder window, open up the Package Contents of your Serviio.app file. (Go to wherever you saved Serviio and right-click/two-finger-click on the app, then click on 'Show Package Contents')
2) Go into the Contents directory and open up the Info.plist file. Copy this file to another location before you make any edits so that you can restore if need be!
3) Scroll down until you see something like
- Code:
<key>Java</key>
<dict>
<key>MainClass</key>
<string>org.serviio.MediaServer</string>
<key>JVMVersion</key>
<string>1.6+</string>
<key>ClassPath</key>
<array>
<string>$JAVAROOT/concurrent.jar</string>
<string>$JAVAROOT/derby.jar</string>
<string>$JAVAROOT/freemarker.jar</string>
<string>$JAVAROOT/groovy-all.jar</string>
<string>$JAVAROOT/gson.jar</string>
<string>$JAVAROOT/httpcore.jar</string>
<string>$JAVAROOT/jaudiotagger.jar</string>
<string>$JAVAROOT/jcl-over-slf4j.jar</string>
<string>$JAVAROOT/jcs.jar</string>
<string>$JAVAROOT/jdom.jar</string>
<string>$JAVAROOT/jul-to-slf4j.jar</string>
<string>$JAVAROOT/log4j.jar</string>
<string>$JAVAROOT/org.restlet.ext.gson.jar</string>
<string>$JAVAROOT/org.restlet.ext.net.jar</string>
<string>$JAVAROOT/org.restlet.ext.xstream.jar</string>
<string>$JAVAROOT/org.restlet.jar</string>
<string>$JAVAROOT/rome-modules.jar</string>
<string>$JAVAROOT/rome.jar</string>
<string>$JAVAROOT/sanselan.jar</string>
<string>$JAVAROOT/serviio.jar</string>
<string>$JAVAROOT/slf4j-api.jar</string>
<string>$JAVAROOT/slf4j-log4j12.jar</string>
<string>$JAVAROOT/winp.jar</string>
<string>$JAVAROOT/xstream.jar</string>
<string>$JAVAROOT/config</string>
</array>
4) Find the lines containing the slf4j* files.
5) Leave the Info.plist file open, and go back to your Finder window. Go into the Resources/Java directory.
6) Right-click/two-finger-click on each of the slf4j* files and click 'Get Info'. In the window that opens, copy the full path to the file (this is found after where it says 'Where:' in the info pane).
7) Go back to the Info.plist file, and replace '$JAVAROOT/slf4j*.jar' with the full paths you copied in the previous step. This should set up Serviio so that it looks at the slf4j*.jars that were included in the Serviio package, and not any other slf4j*.jars that are floating around on your classpath.
8) Post back here with the results!