While I don't own either, I have heard them both at shows and/or dealerships. They have very different presentations, IMO.
The Harbeths are a little recessed in the mids and highs. More of a mid hall presentation, whereas the Definitions are more forward and detailed in the mids and highs. If you like a very lively sound, then you may prefer the Definitions.
Of course, the Definitions (or the Presence) will go deeper due to their active subwoofers.
Based on the volume of your room, the Definitions may deliver more satisfying decibel levels depending on your listening preferences.
However, with the McIntosh amp, the Harbeth's will also play quite loudly.
The Harbeths are a little recessed in the mids and highs. More of a mid hall presentation, whereas the Definitions are more forward and detailed in the mids and highs. If you like a very lively sound, then you may prefer the Definitions.
Of course, the Definitions (or the Presence) will go deeper due to their active subwoofers.
Based on the volume of your room, the Definitions may deliver more satisfying decibel levels depending on your listening preferences.
However, with the McIntosh amp, the Harbeth's will also play quite loudly.

