Midifier is a VST plugin. To use Midifier with a sequencer or audio editor that supports only DirectX plugins you need a special plugin, a VST-DX adapter, which allows you to use Midifier as a DirectX plugin.
We tested the following adapters and they're all working fine with Midifier:
Note: Spin Audio's free VST DX Wrapper Lite didn't work for us, but you may give a try.
The Spin Audio Wrapper and ToneWise DirectiXer have free trial versions. The Spin Audio Wrapper never expires.