MT RB750 and RTP voip ports

I am having a great deal of difficulty getting my cisco hardphone or 3cx softphone to connect to my 3cx sip server through my mikrotik rb750.

i have found the following forum which describes my problem to a tee, i have added the code but not had any success:

http://forum.mikrotik.com/t/correct-way-to-send-support-a-sniffer-file/36812/1

i am getting RTP errors in the logs of the 3cx server:

working from the office at home behind a netgear dgnd3700, i am able to use the hardphone and soft phone with no problems at all.

any help would be greatly appreciated

Note, i am happy to pay some $$ for anyone who can assist in resolving this issue.