When you post you can add photos in the "Additional Options" > "Attach Files" section. Maybe just mention the connections on the 2 32's and the 42. What ever amount you spend, I want to make sure I don't give bad advice based on not enough info.
This is were things get complicated.
1. You have the 3 large displays which each probably has hdmi. But you want a 27inch TB display. As mentioned in several posts, the TB display will narrow your choices to the nMP's (new Mac Pros). This in turn uses more money than you want to spend (8 core nMP $7,300)
2. You can use an 8 core 2009 MP to do music recording. But the 2009 and 2010 MP's dumped the FW400 ports. You would have to get a audio interface that's FW800
3. If you go the 2009 oMP route you also will have to dump the video card (gt120). Since you will need to run all 3 displays you can search for that specifically. 2 cards or if there is a way to run 3 from one card. Someone will chime in on this. There are 4 PCIe slots in the 2009 & 2010's.
4. When it comes to mixing if you use UAD or Waves the SSD will help. Here you will need to place it in a PCIe slot with something like
http://www.apricorn.com/vel-solox2.html This will give you 6G speed with a 6G SSD.
5. 16GB of ram is a good start. Since the 2009's ram is inexpensive you should shoot for 24-32.
6. You may want to get the 1TB HD you speak of as storage for audio files. Use the SSD just for mixing so it does not fill up.
So your set up would look like this:
2009 8core MP 24-32GB Ram
4 internal hard drives- 1.OS 2. 1TB Audio files storage 3. ? 4. ?
4 PCIe slots- 2 video cards (if needed) 1 Apricorn for SSD (Mixing) 1 Another SSD for OS instead of slot 1
Connect all 3 large displays to Videos card(s)
7. Unless you are doing live recording it is better you mix in Protools and just monitor thru the external mixer. Also bypass the Protools plugs too.
Are you using the PF 600 as a midi interface for the Roland? Is the Roland just to trigger? Are you using the PF 600 as a mic pre also?
Well that's enough for now. Will give the nMP people a chance to make their case!