The CA2A is a La2A clone - an optical compressor. The Cake version is very nice.
All the PC4K modules are SSL clones. The bus compressor is, to my ears, really great.
The 1176 module doesn't come as a VST, I think. But the SSL bus comp and 1176 come w/ SONAR Producer. A good reason to upgrade. However, there are a bunch of 1176 VSTs out there. Softube makes one I use instead of Cake's - it is part of their MIx bundle that is adapted for the PC but you can use it as a VST. There are plenty others out there, including some free ones.
If it was me, the SONAR Pro would be the most cost-effective route. You get a good track comp w/ the 1176, a great bus comp w/ the SSL, and a great EQ on every kind of track. And the Prochannel itself, which is part of the inspector, is a great methodolgy to keep track of your channel effects. I seldom step outside the PC, even for delay, which I now have w/ the overloud keyboard fx bundle. There are other reasons to upgrade to Pro, but the PC is a great one.
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