I'm a newbie to Linux audio.  I'm only concerned with audio playback -- I'm not recording or mixing audio and my primary concern is high-quality audio playback. 

I have two questions: (1) What have others found to be the best configuration for sound quality with amarok (output engines, upsampling, et cetera) and (2) Is there any reason to mess with Jack if you're only playing back audio from one source?

My current configuration:
* Ubuntu Feisty running real-time kernel
* Amarok 1.4.5
* Playing FLAC files from a network share
* USB sound card (using the Headroom MicroDAC)
* xine engine with alsa & jack plugins setup
* alsa plugin uses secret rabbit code's libsamplerate to upsample from 44100 to 48000 using "samplerate_best" setting

To me it sounds the same using ALSA without Jack, but perhaps the limitations of my amp/speakers/cabling is the issue there.

I'm no audiofile but I think the purpose of Jack is to give you give realtime audio playback that is never de-prioritized.

So I think... (1) it should sound the same except in (hopefully) rare instances where you have other programs trying to hog all the resources and (2) you really only need Jack for editing audio.