I'm new to the whole music server thang, but I'm a pretty quick study of technological things, so here is how I see it at the moment.
What is the Slim Devices Transporter? It's a device that is intended to stream music from a computer or server to your home stereo system. It includes good quality DACs, an assortment of digital outs, and a basic fluorescent display on the face of the unit to see what's playing and to make other selections. It also allows for streaming of inet radio.
The SD Transporter makes sense when A) your computer / server is located away from your AV rack, B) you use something other than iTunes to manage your music files and C) you need good DACs to process the digital signal before it is sent to a preamp.
Since I use a laptop as my primary computer, which has far too little HD space to hold all the music files I plan to store and I don't use a desktop PC of any sort that would have the space for larger hard drives, I purchased a mac mini and two external HD's to store all of my music files on.
Now I could have tucked the mac mini system away in my den and put a slim devices transporter in the AV rack. Or I could have used an apple TV, or I believe I could even use an Apple Airport to get the wi-fi streamed audio from the mac mini server to my prepro.
However, I got to thinking, the mac mini and the two HD's are small enough to put right in my rack and it cuts out the middleman (a streaming device like the transporter).
Plus, I can send the video out from the mac mini to my prepro (which is then sent to my TV) so that I have a much more user-friendly graphical iTunes interface that I can view on my TV. And if I want to take something like Pandora for a spin, I can do that too. I don't believe the SD Transporter allows access to websites like Pandora and if your rack is enclosed like mine, it would be less convenient to use its fluorescent display as an interface.
Plus, I can expand the ease of use of an Apple iTunes based music server in the future by purchasing an ipod touch to use as a portable graphical interface. This sort of thing comes in handy when you are entertaining guests and don't want to have to go to the room with the TV to make a new selection.
Besides, in my case the much of what you pay for with the SD Transporter (high quality audio components) is at best redundant, and at worst inferior to sending the digital signal directly to my Classe prepro. While it is clear that Logitech has put a lot of effort into making the Transporter suitable for an audiophile system, it just doesn't make sense if you can hardwire the digital out directly from the server to a high-end prepro like the Classe. Logitech is after all a computer peripheral company and Classe specializes in high-end audio equipment. Which one you gonna put your money on for having the better DACs and analog output stage?
Now if you were running a two channel pre, like the Modwright, you needed a good DAC to feed it your streamed music, the SD Transporter is the way to go.