It's very possible that the problem is that your home has too many leaks rather than it being a problem with your HVAC. One of the main symptoms of a leaky home is dry air in the winter.

Visit the Dept. of Energy website along with that of EERE and enrgystar.gov and look at their information on air sealing. This will give you more information on this along with many steps you can take yourself to alleviate the problem.

I would try using hot water. It helps evaporate the water. Many manufacturers suggest using hot water with heat pumps. I found that hot water works well with gas heat also. You should see levels in the 40s.

Mine was ran on the hot water side because I have a heat pump and the air temps are so much lower than a gas unit to help with evaporation.

I have the Trane version of the by pass humidifier connected to my XV95 furnace and it is connected to the hot water. It ran all night and did not bring the humidity above 36% eventhough outside humidity was in the 90's (raining). However I have let it continue running all day and it is still vey humid outside and inside has now barely got to 40%
Key1

I've always prefered the powered humidifier with it's own fan like the Aprilaire 700A.

No damper setting required to assure no moisture blowout, no airflow loss and blower performance reduction due to bypass, no summer/winter damper to remember, increased capacity and output, especiially with hot water.

Why does air handler bring in outside air in the winter? Coastal is right, tighten house will solve humidity issues!