You can’t put analog signals on USB, and the USB spec doesn’t have any variation of the connectors that handle it as far as I can find. Mini-USB B/ USB B/USB A/micro USB, etc, they are all the same electrically: 4 conductors: power, ground and 2 signal lines. But any manufacturer could use USB signalling in a proprietary connector, with other signal types, if they want, as it appears Sandisk is doing in the Fuze.
So any speaker dock that uses the “USB connector” for analog signals must have some proprietary thing going on. I connect to my speakers using the headphone plug. When I plug into my PS3, the PS3 is just seeing an MSC device, recognizes the music and has it’s own decoders for the files, i.e., it uses it’s own internal mp3 player for mp3s.
As for remotes, well, AFAIK, all modern remotes are digital controllers (any one here remember the old high frequency audio TV clicker type remotes?). They generate a unique digital data stream for each button in the Infrared (and you gotta have an IR receiver). I’ve written a number of IR remote receivers for microcontrollers (CD players, DVD players, etc.). Some even use proprietary radio or bluetooth and there may be a wireless USB spec coming someday. A device can certainly support control through the USB, which the Clip doesn’t, at least not in MSC mode (it may well in MTP, but I have never used any MTP device and I am unfamiliar with the protocol). All depends on having the right drivers, of course.
You can do a lot of things through the USB with the right software. Stream digital audio and video, act like a disk drive, network adapter, mouse keyboard, etc. See the device classes section of this article: USB - Wikipedia All of those functions are implemented using digital data through the 2 USB data signals.
Robert
