Phonon is to KDE what PulseAudio is to GNOME. What's more, Phonon beats the crap outta PulseAudio for being simplistic.

I have been a KDE and pro-audio user for about 4 years, and KDE 4 is truly a blessing. Phonon with the Xine backend has proved to be the ultimate environment. I start JACK and two instances of TiMidity++ (one ALSA out, one JACK out) on bootup (as user in realtime with proper privilleges), which is very simply taken care of by Phonon (System Settings > Multimedia > Select JACK as first device for all). It is intelligent to fall to the next device in case of a failure, and then return once again if JACK is running anew.

I have no other server interfering with the flow/chain, and with the ALSA JACK plug-in I can even play games like Urban Terror. However, this is only an abuse test - don't use JACK as a generic sound server! (definitely never meant to be one, though it appears to be able to handle whatever you throw at it)