Yes, you must use the IP agent for Citrix version. The regular IP agent on citrix or the IP softphone will not work. Actually they would work, but only 1 person at a time. If you attempt more, the software will lock up.
The version I used for Citrix is: IPAgentR606476citrix.exe
Then there is also a patch: IPAgentR606476citrixsp.exe
You can download them at support.avaya.com.
Remember you must have the software RTU's loaded on your PBX.
thanks,
Wildcard