i see 2 questions in your post.
1. Confusion about Low Affiniy and High Affinity requests, Jobs and Processes
2. Bad performing reports/cubes
The first one has to do with scaling or sizing of your Cognos Environment ie. How many concurrent requests can my server handle.
All the selected processes have to do with how many processes you allow on the server.
2 servers*4*4 quadcores = 32 cores *2 bibus processes * 4 low affinity connections = 256 concurrent requests can be processed!
2 servers*4*4 quadcores = 32 cores *2 bibus processes * 1 high affinity connections = 64 concurrent requests can be processed!
i don't know how many users you have to support but a configuration like this 2560 active users in your environment and 25650 named users!!
So in theory this seems not the problem to me.
The second question has to do about designing your report and/or cube. Nesting and zero suppression is most of the time killing especially for reports in analysis studio. Most likely you have many categories in the nested level(s).
Ask yourself Do you really need them all?