I too was having difficulty with configuring Phonon to use my external card. After an hour or so of research just one simple sentence from Mamarok at kde.org got things working….
“These settings are now handled by pulseaudio, but you need to install pavucontrol to handle that.”
Install pavucontrol from terminal or synaptic, then search for ‘Pulseaudio Volume Control’ in Kmenu or using alt+F2. Hopefully you will be able to configure your sound card from there.
THANK YOU SOOOOO MUCH FOR THIS POST!
I spent hours trying to get my ASUS Xonar Essence STX to work. I installed and messed with so many things on my pc to get it to work and nothing was ever working and eventually I gave up. A few minutes later I typed "Linux Mint soundcard" on google and started searching around and found this thread with your post.
I registered an account here just to thank you for your post haha.
Encase someone else has this problem and is new to linux here's a step by step guide.
1) Open up terminal
2) Type: sudo apt-get install pavucontrol
3) wait for it to finish downloading and installing.
4) Go to Menu and search "pulse" you shoud find something called PulseAutdio Volume Control
5) Turn on some music (I went to Youtube and loaded some music video)
6) Go to Output Devices. On the right you should see a green checkmark on one or more deviced. To the left of thos you'll see a tiny red X. click the red X on all devices except one (on that one you Green Check it)
7) Then click on "Port" and scroll through all the options. if nothing happens then red X this device and Green Check another one) do this and hopefully your sound will eventually work.
Also my for some reason the sound device that made mine work had the name CMI (some numbers) Oxygen HD Audio which as far as I know has nothing to do with my soundcard. So I was really surprised when my sound started playing (also I heard clicking on my headset while I was changing the ports for this device)