Hi, since you have 0 replies i will tell you what i know.
Yes, multiple FireDTV / FloppyDTV cards to a central server and can be controlled by the client machines if the card is idle. otherwise you can catch the stream that the card is running. (pretty cool

).
Yes, stream to clients, (on my newly vista machine i stream the tv only takes 5-8% cpu power form the server and its not Core2, 3200 AMD)
I have been running MP on windows XP for about 3-4 years, worked grate, some skipping in the Digital TV card video, now i'm trying MP on Vista Ultimate and it look promising, no skipping of the video in TV, but i will upgrade the memory
using 32bit vista(no reason but had the license, perhaps some driver issues with 64bit on the TV card, but untested).
but use 64bit on my own computer.
Correct me if i'm wrong about the FireDTV...