Is it wrong to install both a whole house humidifier and a whole house de-humidifier?
The problem is that your air conditioner is probably over sized or the fan speed is set too high. An air conditioners primary function is to remove moisture from the air. To big of an air conditioner and it drops the temperature too fast and can't pull down the relative humidity. If the fan speed is too high then the interior coil doesn't get cool enough to cause water to condense and drip into the drain. There are a few ways to make the air conditioner do its primary job of humidity removal work better. The simplest is lowering the fan speed. This  link explains some tactics with a little detail. Air conditioning is tricky and it requires many measurements with specialized tools. It's not really a DIYer job but, with enough acquired knowledge anyone can understand it. Lots of installers and service techs don't actually know what they are doing. They often set the fan to the highest available speed, install the largest equipment possible, charge the system with the beer can cold method and generally accept that if it's blowing cold air it's perfect. That is not the case. Get a good, reputable service tech over and explain the issue. You don't need a dehumidifier, you need to set up the one you have. A good tech will have your house cool and dry in no time. 

I'm from Toronto, we get a dry -40°F to a very sticky 110°F. If we can get by without dehumidifiers here, you can in Pennsylvania.