Hi dainis,
You are right for high speed emulation.
I've searched a little and found that most of mp3 player fitted with HDD as storage media, don't take full use of IDE and ATA features. Hence, I still believe that for this kind of application, and only for this, you can still do "reverse direction of ATA conector" in one word, emulation.
But, like you mentioned above, real high speed emulation it's not possible without using special controller IC from HDD or FPGA. Thus, the kyndal's presumption that emulation an harddrive through network, could be used in many cases it's not full sustained by the emulation I'm talking above as still possible. He still needs those circuits mentioned by you and another design approach.
I agree with you that more simple and real is making new network (ethernet and TCP/IP) based MP3 player, rather than maping IDE sectors through network.
Really madness. Less headache if the complete files are brought in the local cache and fed to mp3 core.
The only concerned is accessing the network and if the privileges are granted, to extract the required mp3 file.
Yes, this design approach is much more viable.
silvio