The Pain of Syncing iTunes Libraries

I have a problem.  I really hate the manual process that I have to use to keep my two iTunes libraries in sync, and I'm dying for there to be a application that solves this problem for me.  There are quite a few that synchronise iTunes libraries between machines, but I'm not confident that any of them really do what I want.

The libraries are on two Macs; a Power Mac G5 and a Macbook Pro.  The Power Mac sits at home, has lots of disk space, and contains the 60Gb master version of the library.  However, I am often away from home, and so the Macbook Pro is my day to day iTunes machine, but it has a lot less space, and only has room for a 20-30% subset of the library.  Oh, and this is the version that gets synced to my iPhone where I do quite a bit of listening.

When I add tracks on the Macbook Pro, I have to remember to manually copy them to the Power Mac, and sometimes vice versa.  The copying process doesn't take account of ratings, play counts, or other metadata.  Large chunks of my main music library go neglected, because they never get onto the Macbook Pro. Et cetera. Et cetera.  So, I want an application to synchronise music between these two machines.

Here's what I want it to do:

  1. I want a selection from my master library on the Power Mac to be synced to the Macbook Pro;

  2. I want the mechanism for determining what is in and out of this selection to be at least as flexible as the iTunes smart playlist. This is so that I can do things like automatically rotating songs that I like, but haven't listened to recently, into the Macbook Pro's version of the library;

  3. I want the sync process to remove tracks from the iTunes library and hard drive on the Macbook Pro if they become removed from the selection on the Power Mac;

  4. I want the syncing to run automatically in the background over the network.  It would be nice if it worked over the internet, but over wifi is the minimum requirement;

  5. I want songs that I buy or otherwise add on the Macbook Pro to be synchronised back to the Power Mac.

  6. I want metadata to be synchronised.  Particularly, in addition to the basic static info like song names, albums, genres, artists, etc., I want play counts to be accurate on both machines, rating changes to be synchronised, and the various dates to be right;

  7. I want it to work while iTunes is running;

  8. I want it to be secure and not provide the general public with access to my library.

It's not clear to me that any of the existing products that do this kind of thing are able to meet all of these requirements, and I'm not sure why.  Perhaps I'm unusual in what I'm trying to do, or perhaps there are technical issues in here that just can't be solved with reasonable effort.  Perhaps I'm just not understanding properly what I read on product websites.

So, am I crazy to want this?  Is there anything out there that does it?  Help!