Definitely play around with your matrox unit first, see if you can find any joy out of it.
Im assuming powerdesk has not helped? (Even with powerdesk my 7970 has max 1360x768x3, now i know why!)
The mview unit i am going to get for myself is the MV103-HDVE Pro
http://www.mviewtech.com/listen.asp?ProdId=111025101735(for my 3x7970s running a 3x3 video wall, i have 22" Dell LCDs atm but will upgrade later to 32" or 40" TVs) because i already have 2x TH2G Digital SE (dp in with 3x DVI out) and my TH2G digital Edition (DVI in) wont work with powerdesk (So im locked in @ 1280x1024 max).
The price is about $275 US inc. shipping but may vary for you (Im in Australia). Here is the link:
http://www.dhgate.com/product/mv103-hdv ... |624194340If you have questions about compatibility, etc... you can message them on their site and they will respond (I was impressed) or PM them here on the forums, here is a link to one of their posts:
http://www.wsgf.org/forums/viewtopic.php?f=67&t=25146PLEASE NOTE i have not actually purchase one yet but like I said after burning coin on matrox (Thanks for showing me the compatibility guide, I seem to keep learning the hard and expensive way!) the mview boxes seem MUCH better, the Pro versions have cascade functions (multiple boxes stacked on eachother, checkout the diagram tab!), 1680x1050x3 @ 60Hz is supported and are slightly cheaper than matrox. I would have bought these instead if I knew about them at the time.