The Rio Reciever doesn't bother with ripping CDs or creating MP3 files of its own, it streams them from either a Rio Central, or a Windows box with their software installed. Either method allows you to setup playlists which are then accessed from the Rio Reciever.
Hooking speakers up to the receiver is easy. It has bare wire outputs for going directly to speakers, RCA outputs for use in a stereo rack, and a plain old headphone out that's suitable for most powered PC speakers. That's a lot of outputs, but it means that it's easy to use in a variety of situations, which is exactly what you want out of a device like this.
The reciever can reach its source through either an HPNA jack, or an ethernet jack. Hooking up the Rio Reciever via ethernet was fairly simple, provided a compatible server is already on the same subnet. The receiver finds an available IP address- although it seemed to ignore our DHCP server and actually took our routers IP once! This isn't a fatal flaw, but you may wanna double check when you set this thing up to make sure you don't get any surprises.
The interface on the front of the box takes a little getting used to. Menu items are selected from menus by a large dial, and confirmed by pushing the dial. (which also functions as a large button) While compact, I found that all too often I'd accidentally push the dial in while trying to turn it. Eventually I had to give up and stick with the remote control which didn't have that problem.
Unfortunately, while the interface isn't bad, it's not great either. Given the sheer number of MP3s available to play, navigating through a huge list with just a dial isn't fun. If you've put the time into make playlists using either the Windows software or the Rio Central, then this is much easier. Of course you can search search on artist, album, genre, etc., but it gets more and more difficult as your MP3 collection gets larger.
The screen on the receiver leaves a lot to be desired. Unless it's at eye level at a distance of six feet or less, don't bother trying to read it. Luckily once the player is rolling, there's little reason to bother looking at it. When first installing, I got a neck ache from trying to read it while it sat on my desk, but once up and running, I became oblivious to it.
The Win98 software is very bare bones, but does what it's supposed to: import music. After installing the software and turning on the receiver, I was able to import both MP3 and WMA files.
The functionality of the Rio Receiver does not change between the Rio Central and a Win98 Machine, so for those who already own a windows PC, they can possibly save themselves the $1500 cost of a Rio Central. The Rio Receiver is priced around $170, and a couple discount places have already had them priced around $100, making it very feasible for the home audio enthusiast who has a large music collection on his computer to pop these small boxes around your home or office, letting you share your music wherever you want it.
The SliMP3 is less polished, but is fed with a simple perl program that streams audio. The Audiotron is fed with any Samba compatible server. In other words, either device can work with a Linux box. The Rio currently can't, but it is the only one that doesn't require an external amp to hook it up to speakers, making it the best choice for simple multizone applications. And it's priced a hundred bucks less!
All in all, this is a pretty neat device. I wish it had more ways to stream MP3s to it, since buying the costly Rio Central or converting my MP3 server to Windows aren't things I'd consider at this point, but for a lot of users I imagine the Windows software will be enough. Unlike many MP3 units, this one is priced reasonably. The variety of input and output options mean this thing can work for people who just want to get their MP3s into a stereo component, as well as for people wanting to create a nice multizone audio system in their house without needing a second mortgage.