How do I add multiple entries of the same item in subgrid?

Hi Guys, 

Here’s what I’m trying to accomplish.

I want to create a new Tab in the Accounts form where in I can Add multiple “Items”. See sample layout below.

Here’s what I’ve managed to do so far,

1. Created a custom entity for the hardware type
2. Created a N:N relationship for the hardware type and accounts
3. Created a subgrid on the account forms with the data source entity as the hardware type entity I created in #1

Here’s where I need help.

I can only Add 1 entry for “Hardware Type” for each account. How do I allow multiple entries of a hardware type for each account?