do you have to plug a wireless thingy into the PC?
Yes. It comes with a wireless "antenna" that you plug into your USB port.
WIll it work with an existing wireless network?
No. It's not 802.11. It uses "HomeRF". According to the documentation:
"simplefi uses HomeRF wireless Ethernet to connect to your home PC. With this system, you don't need to install wires or move your stereo. Future versions may support 802.11b, 802.11a, wired Ethernet, HomePNG, HomePlug and other networking technologies."
As far as distance between the home PC and the simplefi hardware:
"Approximiately 150 feet through walls."
Can you play music from more than one PC?
You can use a single PC to play to multiple simplefi devices simultaneously, and what they play is independent of each other. So I can play Billy Joel in the living room and Pet Shop Boys in the bedroom (and have). I imagine that MC could use Zones to define the different rooms and you could have playlists running in multiple locations.
Each device obtains an IP address (though DHCP) and there's a security code that you can add to both the network adapter setup and the simplefi hardware so you're sure that you're safe from prying eyes.
The unit supports MP3 up to 320kbps and software (and firmware upgrade) came out several months back which added WMA support.
One feature I really like is a feature called "TagIt". If you're listening to a song over Internet Radio that you like, you hit this orange button which "tags" the song and stores the song name and artist on a website that they give you access to. It makes it really useful to go back to songs later that you listened to throughout the day.
Here are some useful links that may help.
Sales info
http://broadband.motorola.com/consumers/products/simplefi/QuickStart Guide (PDF)
http://broadband.motorola.com/consumers/products/simplefi/downloads/simplefi_QuickStart.pdfUsers Guide (PDF)
http://broadband.motorola.com/consumers/products/simplefi/downloads/simplefi_installation_user_guide.pdfNote: This users guide available online is based off of the version of the software prior to a firmware upgrade that now allows the device to support WMA. Some minor changes were made to their desktop software components as well.
Installation Addendum
http://broadband.motorola.com/consumers/products/simplefi/downloads/simplefi_installation_addendum.pdfThe company that produces this is:
http://www.simpledevices.com/I am in no way affiliated with SimpleDevices or Motorola, just an MC user that would love to wirelessly stream music to my home stereo. If you have more questions, please let me know.