Remove the quotes around what you typed and add a /C.
Here's what I have:
C:\AGTH\agth.exe /C "blablabla"
Edit: Oh, and for some games (like this one), you won't be able to get all the text unless you type some more stuff. I mentioned this earlier; you'll need to enter
C:\AGTH\agth.exe /C /x3 /kf /ks /c "blablabla"