A pre-amp with multiple simultaneous outputs.

You can always look into a good multizone reciever to use as a pre-amp. The Denon 3805 is relatively inexpencive and gets great reviews. I own one and am quite impressed with its performance.

Not sure of the specifics of your scenerio, but say you want to have 5.1 surround in the living room, 2 channel in the basement, and 2 channel upstairs, you could use the 2nd and 3rd zone pre-outs and connect these to the pre-amps upstairs and downstairs. Say you have a listening room in the basement, you could always keep the gear for serious listening down there, but tap off the Denon3805 when you desire.

The 3805 can either do 7.1 with pre-outs to the 2nd or 3rd zone, or you can do 5.1 and power another zone off the reciever and do the third off another pre/amp, or even skip the additional pre and just use an amp.

Radio upstairs, 5.1 DVD in the livingroom, and CD in the basement all simultaneously.

Then again, if yer using Levinson, Rowland, Krell, Edge, or other gear in that price range, this might not be the way to go. I suggest you try to hear a 3805, its about as close to the sound of seperates as you can get without getting seperates, and would definatly have the capabilities you are looking for.

The manual for my PS Audio PCA-2 explicitly mentions using multiple outputs at once, and it works fine (I'm using one output to main amp, one to subs). I've also used multiple outputs simultaneously on my Bryston BP-25 (two sets unbalanced, one balanced). I've also used high-quality Y-adapters to split a single output, again with no problems. Generally, the only issue is that the amp (or 2nd system) inputs be of reasonably high impedance.

For your application, you may want to find a preamp with a buffered tape output, and use that instead - that way, volume in the 2nd system will be affected only by the local volume control, not by the main preamp volume control. I've actually done this, but not with such a long line.

You may want to use a tape output and a line driver. Van Alstine makes one, and if you go to balanced lines (maybe a good thing with such long runs) there are a number of relatively inexpensive pro-audio options for a line driver.

Finally, I'm now accomplishing something similar to what you want to do by using a Ramsey FM transmitter from the tape out of the upstairs system, and tuning in downstairs. Pretty good sound quality, certainly fine for background listening downstairs.
Rich