The Mojito is basically an "internal MXO2", and is almost identical in features to an MXO2 LE with Max. It does cost less to go Mojito, but you lose the breakout box and get a snake cable for i/o instead. Do you require SDI video and XLR audio? Otherwise an MXO2 Mini Max might suffice, with analog and HDMI i/o.
We use Asus motherboards and Intel Core i7 processors in our Matrox/CS6 turnkey systems and get excellent performance. The MXO2 units are not very fussy about the PC hardware the way the old RT.X2 and RT.100 boards were. If you build a nice system for Adobe, Matrox should fit right in.
Here are Matrox requirements - http://www.matrox.com/video/en/support/windows/mxo2/system/requirements/
Adobe recommendations here - http://www.adobe.com/products/premiere/tech-specs.edu.html
Basically, a Core i7 with 8-16GB RAM and an open PCI-e slot, running Windows 7 Pro 64-bit. Nvidia display card recommended to get the GPU acceleration in CS6, and 2-drive RAID 0 array for video storage. If you want to use a 6-core processor, or even go dual-Xeon, should be fine, but the 4-cores work great for Premiere.
Safe Harbor Computers
[moved to hardware forum]