How exactly is Task Manager telling you how many processors are in use? Are you going by the eight "CPU Usage History" windows?
The NumLogicalProcessorsUsed property says that all 8 processors are being used by the server... if there is no work for them to do, Task Manager won't show anything in the "CPU Usage History" windows.
Your problem probably has NOTHING to do with a shortage of processors, or an unwillingness by SQL Anywhere to use the processors. It probably has some other explanation, like (possibly) all the connections are blocked by a long-running transaction.
Please answer the question "Are you concerned about performance of multiple connections, or one single connection?"
Do not assume there is a bug in SQL Anywhere, or focus on some unproven explanation (shortage of processors)... look at the connection activity. Use a monitor like Foxhound, or check out the Performance and Tuning article in the wiki.