Mokoena's transfer to Wits has been held up over his demands for £600,000 (+/-R7.8-million) to rip up the final 12 months of his contract.
The amount includes money owed to Mokoena, as well as compensation for the remainder of his contract, now around £10,000-a-week after a relegation clause was triggered.
Tal Ben Haim and Kanu are in a similar situation.
Birch recently criticised the players' stance, saying that unless they accept a compromise the club will go into liquidation.
The club return for preseason training on Monday, and Birch tells Portsmouth.co.uk he is hopeful a compromise can be reached.
"I am still talking with Aaron’s agent in terms of an agreement compromise," he said. "I would say at the moment it is going okay. We are continuing to talk so you have got to be hopeful an agreement can be reached.
"As before, we need to remove players from the club's wage bill and are working hard on trying to achieve that.
"Conversations are also still going on with Kanu and Tal Ben Haim. Agreements must be made because time is running out."