Please note that the system requirements mentioned in the Installation guide are the Minimum requirements to install the product. The actual requirements could ( and usually is) higher than this, and it entirely depends on the usage.
As mentioned by Girish, it really depends on your requirements.
Will the repository DBMS run on the same AIX box? In the same "physical" network segment? Somewhere else?
Will the primary source/target DBMS run on the same box?
What data volume do you expect in average / peak times?
What reaction times have been set in the SLAs for average / peak data volumes?
How large are the records usually processed?
How complex are the transformations?
What "external" logic do you use heavily (such as Stored Procedures in some DBMS, standard auditing sessions, and the like)?
We can give you all sorts of estimation, but in the end it might well be that all these won't help you. Simply because you may have completely different needs.
We need information from you to help you decide a reasonable hardware setup. MUCH information.
So you might want to hire someone experienced with such setups for a thorough and reasonable estimation.