When you run the Mapped Key Wizard, you can set a Target. This is the recipient of the keystroke.
So if you run the Mapped Key Wizard, select a Straight Key Broadcast, use you 6 Key, and then change the Target to the Slot of the character you want to receive this keystroke, and then Finish.
You can do the same for 7 too.
If you are using the Standard menu (green boxes), then these will be configured already to use the keys 1 to = (the row on you keyboard) as hotkeys, so 6 and 7 would already be in use.
If you wanted to use another key to send a 6 to a specific window, let say F5, then you can use a Key Remap. This will let you use F5 as the input, and 6 as the output.
If you wanted to press one key, lets say F5, and have this send 6 to one window and 7 to another window, at the same time, then you need to do some manual setup too. The easiest method is to start with the Mapped Key Wizard, and setup the first step, so in this case a Key Remap using F5 to send 6 to a specific Target.
Once you have completed this part, you then locate the mapped key you just created. Select the Key Map in the top left pane, in the lower left pane find the mapped key you just created (look for the Hotkey:F5), and then select Step 1 in the mapped key (click on the plus in the lower left to expand the mapped key), and then on the lower right, right click on Actions, select Keystroke Actions -> Keystroke Action, and then when it adds the new action, set the properties of the key to send to the game (7), and the Target to receive that keystroke. Sounds complicated, but once you do it, it's not really.
There is a video on setting up
Mapped Keys which should help you understand what is going on.
You can also peruse the WIKI. You need to start at
Key Maps and then look through a few of the relevant links, like
Mapped Keys, and
Actions.