Actually, all other things being equal, a 'digital' system will sound better than analog, for example were the Promedia 5.1 to have an external decoder, they would probably sound better than if they were connected to a soundcard via analog. The reason is that the digital to analog converters in external decoders are usually of better quality, and are isolated from the electrically 'noisy' environment of a PC. The problem, however, is that some digital systems compromise the quality of other components to keep the price down. So for example the DTT3500 will have a cleaner D/A conversion because of its external decoder, but the PM 5.1 will still sound better because the amp and speakers are of better quality. Simply put the overall quality of the system makes a bigger difference than the external decoder.
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