I’m so sorry Wheaten it’s my mistake 
the option -O of wget must be capital letter
I correct the initial post
Edit :
Ok forget about it, wget seems broken, please find the plugin as attachment
transfer it via filezilla in /home/volumio
then in terminal ssh
volumio plugin install dstmmix.zip
rm dstmmix.zip
dstmmix.zip (206.0 KB)
Edit 2 :
Ok i’m sorry, in fact it seems to work only if i’m in my plugin git tree, and not from /home/volumio
strange I still need to understand why, but you can try by your side we never know…