Process priority on OSX

Hi,

We are using LispWorks on OSX for some real-time programming (music).  
We are using a process (using "mp:process-run-function" kind of API to  
create it) that is supposed to execute some event handling. Timing is  
no reliable if LispWorks is not the top-most application. We get huge  
delays in event handling. We tried to change the process priority  
either at process creation time with the :priority  keyword or using  
the "mp:change-process-priority" function without any visible  
improvement.

Is there a way to get better timing in LispWorks on OX?

Thanks

Stephane Letz