Yes, it works, but it strains the processor. Onboard sound requires the processor to play back the sound files associated with the game. A sound pack (as I understand it) then increases the load as the processor now has to process higher quality sound files. Sometimes the processor can handle the load, other times it causes the famous jitters and lag. The less work the processor has to perform on sound, the more it can devote to the game thus making your flying experience a little more enjoyable.
If you were buying a desktop, I would simply recommend you buy yourself a PCI sound card as that would eliminate the load on the processor (you might have seen some of the threads regarding sound in the past). Many players in the past have had great success adding a sound card to their system. I'm sure if some are around they can describe the difference to you on the, "Before-and-After" spectrum.