You can use your existing USER accounts
If you have existing GetResponse and ClickMagick user accounts, you do not need to create a new one. Simply submit your System with your existing accounts.
USER accounts vs. AFFILIATE accounts
There's a big difference between user accounts and affiliate accounts:
The user accounts are the one we need to build your DFY System for you. These accounts cost you money i.e. you need to pay for these accounts.
On the other hand, the affiliate accounts are the ones that you created to unlock your Multiple Income Streams. These accounts are 100% free i.e. you get paid from these accounts (not the other way around).
Do I need to invest in GR & CM to earn from them?
No. You will earn from GetResponse and Clickmagick as long as you have an affiliate account (which is free) and set it up in your Multiple Income Streams Step.
This has nothing to do with the DFY System... you will earn from GetResponse and Clickmagick regardless of whether you choose to set up your DFY System or not.
So why would I set up my DFY System?
To build your email list. Read this article to decide whether the DFY System is for you or not.