The reason is because properly done computer based audio/transport is more 3D sounding. Every CD player or dac/transport I have owned sounds flat in comparison. The other big area of improvement is less, far less digiital noise. You don't even know its there until it is gone.These are the two big improvements found with properly executed computer based transports. Like turntables however everything matters and to achieve this sound one must read up and be educated.
The improvement was obvious and immediate to me based on my history with traditional digital. I was not a believer in computer based audio and held out mostly out of fear and ignorance to be honest. Well, I decided to stretch myself and the sound on the other sides indeed better, Yes, it takes work and effort and knowledge.
Those who have truly broke through universally experience what I have stated above. It will only continue to get better and better so go,ahead and start learning. A,aging sound and just as amazing convenience.
Transport and CD players still sound wonderful and I love them. I am just saying it as it is.
FYI, yes I have owned or listened to all of the top, most respected players like the top of line Ayre, Cary 306, $8,000 Esoteric, highly modified Sony SACD player etc.....had belt drive transports with very good dacs. Yes, they all sounded wonderful, but they take a back seat to computer based audio done right. I liked the Marantz SA7 and my TRL modified Sony the most for the analog type sound, but not as good as computer audio.
Steve of Empirical Audio can tell you the technical reasons and has done so numerous times in threads here on Agon. Read his stuff and learn. Great stuff and he has put in the hours to become an expert.