Hi Nev,
Sorry about the slow response. I ended up down at LIMS over the weekend hunting for new products last week, so i've not be able to look over this thread till now.
Your right in what your saying on the first post about the monitors and resolutions. I wouldn't say that a 28" would be blocky by any means, but you won't be getting any more screen real estate over a 24" with the same resolution and yes everything will just appear to look bigger without giving you more desk top.
If you had the room you could go with 2 x 24"s on top of what you already have (a total of 4 screens!!!) and use one of those for xite's mixer panel and split the devices and routing panel off onto display number 4.
Once you go above 1920 x 1200 you have to step upto duel link dvi (the 8400gs is one of the few budget cards that support this) and that maybe why a lot of firms cut off their resolution support at that level as you need to be shifting a lot of data when you go above that level (Wiki on Duel Dvi resolutions -
http://en.wikipedia.org/wiki/Digital_Visual_Interface ).
Ahhh...
Now i've read post number 2, it looks like your already on top of that solution. I wouldn't worry about bandwidth unless the's a lot of 3d data being thrown about (which the won't be whilst working with audio) so you should be fine running those 4 monitors with 2 cards and using the hardware/software apps you require.