I believe I understand the issue. The behavior you are seeing is correct, because an individual FX chain can only hold up to four algorithms. If you've already got four in one FX chain, you can't add more.
I think what you need is to add more FX chains, so you can have up to 16 algorithms across a maximum of 4 FX chains. To do this, go to the FX chains tab (clicking "FXCHAINS" at the bottom of Emote) and drag in a new FX chain from the list of chains on the left, Then, you'll be able to add up to four algorithms on each FX Chain you add.