I used to biwire a pair of Hafler 9270's, years ago. They have a switch on the back to convert to mono (400w), or stereo (135w/c) operation. When used as monoblocs they sounded extremely harsh and brittle. They did play louder. I prefered to use stereo operation, one amp feeding L and R woofer connections, the other amp feeding L and R midrange/tweeter connections on the speaker terminals. If you have a pair of stereo Levinson ML9's, I suggest you consider using them in that manner rather than converting to monobloc operation.