As I understand it, you say you are able to stream content (from your phone) to the Airport Express, and have it output to an amplifier. (Music in your phone -> APEX -> amp -> speakers)
DLNA can do this too. My phone is DLNA compatible, so if I had a media player (Eg : Asus O!play) connected to my amplifier, then I can stream music to the amplifier through the media player. (Music in my phone -> O!Play -> amp -> speakers)
The advantage of DLNA is that if the content is on a device on the network (Network Attached Storage, Computer, another media player, etc) that is DLNA compatible, I could stream that content to the media player and out the amplifier. (NAS/PC/O!Play/etc -> O!Play -> amp -> speakers, controlled by DLNA phone)
The Apple ecosystem can also do the above, but the source on the network must be iTunes. (iTunes -> APEX -> amp -> speakers, phone controls iTunes)
DLNA can also stream content from the network to the phone. (NAS/PC/O!Play/etc -> phone (listen on headphones?))