Cool, further investigation and I am ruling out the Steinbergs (UR22/44) and The Focusrites.
The Steinbergs as they are very similar to the Tascams and the Tascams come with X3 LE (Which I probably won't use but I certainly won't use Cubase AI!) and the Focusrite as it doesn't have a hardware DAW monitor/input mix knob, but only a software one. (Shame as the 6i6 looks quite good!). The Steinberg UR44 doesn't have one either.
 
So, down to Tascam or Behringer, 2 inputs or 4.
Best Prices I've seen:
 
Behringer UMC204HD  £66
Tascam US-2x2          £100
Behringer UMC404HD  £85
Tascam US-4x4          £158
 
Anyone actually used the UMC404HD with Sonar? (Or in fact, the Tascam 4x4?)

Im still very happy with windows 7 64 bit and believe you will will be as well!  
 
As far as which version of sonar to consider - definitely demo a few things.  The top 2 are extremely functional - and the lifetime membership means this is the best time ever to do it. Ive been a very happy platinum user for a few years, I do believe it is worth it.
 
My first reaction to your setup would be to try going for an interface that will allow you to have all your awesome synths plug directly in, bypassing the 1202.  Its very possible that the preamps and summing you currently experience will be restricted by the mackie, as well as outperformed by a more modern interface and in the box mixing. 
 
As far as hardware - I would lean - personally - more towards the tascam side of this conversation - as I have used many of their products in the past.