If found that the DLNA client is not updating correctly the advanced options, namely the selection of the soundcard.
Digging a bit into the scripts I found out that the /etc/init.d/gmediarender script has an error that is solved modifying line 33 like this:
-ALSA_DEVICE=$(grep -a „GMEDIARENDERER_ALSA_DEVICE“ /opt/max2play/audioplayer.conf | sed -n -e ’s/^[A-Z_]*\=//p‘)
+ALSA_DEVICE=$(grep -a „GMEDIARENDER_ALSA_DEVICE“ /opt/max2play/audioplayer.conf | sed -n -e ’s/^[A-Z_]*\=//p‘)