How to sync iPhone music from 2nd Mac? (don't read this if you own 1 Mac)

Question

If you don't own two Macs, please don't try answering this post with guesses. I need to find someone with real world experience to solve this problem:
My contacts and Calendar are on my laptop. My music and videos are on a Mac Pro. I have disabled automatic sync on both Macs. I have unchecked music and video on the laptop and unchecked the contacts and calendar on the Mac Pro, yet everytime I sync to the laptop, it deletes my entire music library without warning. With video, it gives me a warning when I uncheck but no choice other than to delete video or use what's on the laptop.
There seems to be no way to keep the music and video that I sync-loaded from the Mac Pro.
Interestingly, when I do sync to the Mac Pro, it leaves the contacts and calendars from the laptop alone.
So how do I achieve the same for syncing music and video from one machine only without the other erasing it.
Please don't guess at solutions here. I want to get an answer from someone who has actually succeeded in doing this.
Thanks!

Answer 1

I absolutely am not trying to combine two iTunes library! I thought this was clear so allow me to clarify in no uncertain terms.
Mac Pro contain all my music and video media.
Laptop contains all my contacts and calendar.
Both iTunes have the automatic sync disabled.
The Mac Pro boxes for music and video are checked and none other.
The laptop boxes for contacts and calendar are checked and none other.
In another post, "Qsilver" says it will work, but my experience (and other folks experience) is that when I go to the laptop, all media files are dropped even though the media is unchecked on that machine.
Apparently the jury is still out on whether this can be done or not, so I'm leaving this post open for further discussion.