The answer should be that both the Digital out (SPDIF) and the main Analog out should be active at the same time from your motherboard.
You might have to go in the drivers and activate the SPDIF out. I would imagine that the main analog sound out would be active with sound unless something was done to turn it off, and even then I don't know if you can actually do that. Some systems allow this output to be on the front case of the computer as well, and you can plug in the speakers, and many headphones.
The onboard audio systems on motherboards are not considered well in the audiophile world. There is a lot of electrical going on in the midst of the audio circuitry, adding noise and distortion. The SPDIF both optical and coax on most all of these units is designed for delivering Dolby/DTS audio to a multiple speaker system (DVD movie audio) and delivers it at the 48 khz frequency that DVDs use. Stereo music, from CDs comes on the default frequency of 44.1, and the ubiquetous onboard sound cards do not allow you to turn the frequency down to 44.1. Therefore, the circuitry within the sound chip "resamples" your music from 44.1 to 48, raising another complaint in the audiophile community.
Your options are to just use the onboard sound for your music listening, from speakers and headphones, which might sound just fine to you. Try not to let preconceptions from some of the harder audiophiles here prevent you from having fun.
Obviously you could spend more for a different sound card. A search here for the AV710 will describe a very inexpensive card that will have a "good" SPDIF out. The various drivers for this card, and the proponents of each, if you read over everything here, is great for an afternoon headache break.
The M-Audio Transit will provide a "good" SPDIF out, as well as an analog output for your speakers. Not expensive, and recommended well here on this board. I am in the process of comparing the Transit to more expensive options in the USB -> SPDIF arena. Until I decide which way to jump, I will probably just use my motherboard SPDIF out.