I want to be able to make a macro to update the list of music being served. I have about 20 computers currently on the network with music, but people turn them on and off so it displays different ones each time. Thus, I can't figure out a way to automate this...

You might want to look at the Java-based JReceiver software as an alternative. Perhaps it can update new music on the fly, or perhaps its code can be modified to do so.

Is it possible to append/insert/replace songs to those in the current playlist as in the Empeg? i.e. create playlists on the fly?

Not in the current software. But that is one of my favorite features of the empeg-car, so I hope the empeg team is looking at this and sees that we'd like to have it for the receiver. In your particular situation I can see how it would be almost critical.

Is there any way to use more than one criteria to pare down a list of songs? There's a lot of crap music in the house. Some Simpson's sound clips for example, are listed under Rock music. I can't add all Rock music without getting Bart yelling stuff. Something akin to Wendy Filters would be perfect.

As you said, stricter tagging would have to be enforced. We could talk all day about possible features to filter the music, but when it comes down to it, the player can only tell what the song contains by looking at its tag. So if the tag is wrong (listing a soundbite as "rock" for example), then all the filtering features in the world aren't going to do a bit of good.

The only other way I can see to pare down the lists is to use playlists. Those work quite well on the Rio Receiver. I almost exclusively play from playlists on my Receiver, rarely do I have it shuffle all music or all of a genre.