My TV is the same way in that it must cycle through inputs. Unfortunately, many TV's are setup this way. Direct input selection with discrete buttons is a much better method.
Not all is lost, however. I have a Harmony 688 and, while I did not have any problems setting mine up, I may be able to provide some insight. You may have to fix it by going into your remote setup and editing the "Watch TV" function.
Go to the Watch TV setup and click through, keeping the options the same, until you get to the last page where it asks if everything is correct. Select, "Yes, but I want to add more control of options and devices for this Activity."
You will have to click through all the screens again. At the "Please review the actions for your Watch TV Activity:" screen you can manually add actions. According to my test setup, in which I added your TV, your TV may support direct input selection even though the original remote does not.
Under "Start Action", click "Add". Click the "Send this infrared Command:" dropdown box and select "InputTV", or whatever input you use for cable. I see there are other actions available for your TV such as "set input state to AV1", etc. You may need to fiddle with those settings but it should be rather straightforward.
If this doesn't work, I would contact Harmony support. Though I have not needed to contact them, I hear they are very helpful and they can actually log into your account and fix the problem.