[Solved] Is it my soundcard?

Hi,
I'm using Asus xonar d2x soundcard. my problem is I got this error message whenever I change the setting for using 'direct source' as default audio device:

"An audio device was disconnected or reconfigured. Verify that the audio device is connected, and then try to play the item again."

There's no problem when using digital output. I've tried with other speakers to rule out speaker problem but the problem persists. Should conclude that my soundcard is the problem?
FYI, i'm using win7 x64 and i've installed the latest driver.

I think i need to rephrase my question.

My speaker, logitech z5500, can support both analog & digital input. When i try to switch the input from analog to digital or vice versa, in the same time i have reconfigure my sound setting in the control panel. It used to be okay to use both analog and digital input (not in the same time) without any problem. However, now i can only use the digital input. Whenever i try to use analog the following message will appear:

""An audio device was disconnected or reconfigured. Verify that the audio device is connected, and then try to play the item again."

Sorry. I made a very stupid mistake. I just forgot to uncheck the 'SPDIF out box' in the Asus audio center.

But then i realised that i can use both 'Asus xonar audio device' and 'SPDIF pass through device' (playback devices as seen in control panel) for digital output. Anybody knows what's the difference between these two? What i've realise so far is that when listening to mp3, no sound comes from center speaker if i use the former (asus xonar audio device)one, unlike SPDIF.