Yes, you can use an existing Macquarie CMA into Stake.
You will need to complete only sections 1 & sign section 6 of the attached Third Party Authority Form, which grants us general authority over the account. This allows Stake to arrange the transfers from your CMA to your US trading account - inittaed by yourself using Stake. It also means you can see the balance of that account in Stake.
Once complete, please scan and send back to us at email@example.com