You've done all you can on the H9 – the problem is that you are feeding it a very high input. Your only options now are to reduce the input signal level, either by adjusting it at the source, or using a pad of some kind. A pad can be essentially two resistors.
The problem is that the H9 is designed for a guitar input, not a hot line level. In hindsight, we should have added the line level switch that the 'Factors have. But, there were probably reasons why we didn't.
