John
SNP Productions Ltd is an MTRON and OCZ SSD reseller. We have a custom drive adaptor plate that allows a 2.5 in drive to fit a standard MacPro 3.5in drive sled. OCZ are more cost effective than MTRON currently. Do contact me for pricing.
Re TH2G - for a 4 output system, you may find it easier to use two Dual-Head-2-Go units, or simply One Triple-Head-2-Go + one graphics card output. Also consider the Datapath VSQ-01, depending upon the resolution you require: http://www.datapath.co.uk/vqs01.html
(we also supply Matrox & Datapath)
Let me know if you need to try-out any of these configurations
Regards
Simon