For what it's worth, I have heard the M40 driven by MC402(forgotten the preamp but it's a Macintosh as well). Mcintosh goes very well with the M40 and M40.1 as with any other speakers. If you listen to a lot of natural vocals, some orchestra and favor a sound that is free of listening fatigue, the Harbeth is a good choice. I agree with Tvad's assessment that the Harbeth can be slightly bland in comparison to some other speakers which offer higher resolution of detail, punch and drive, so it's best if one can listen to these speakers before making a decision. I have a friend who loves the punchy and uncolored sound of his PMC EB1i driven by Bryston 4B-SST and describes the Harbeth SHL5 similarly as what Tvad has. Voices also sound good on the PMCs but more organic with a slight tinge of warmth with the Harbeth. It may be due to the different sources that we used as he was using a Mac connected to an Ayre DAC while I had an analog rig hooked up to the Harbeth. In the end, two different kind of presentation and sound on two different setups.
I have not heard the Zu's so no comment there. Nevertheless, if you want a speaker that you can sit down and listen to for hours until you fall asleep on the couch this is it. The Harbeths are very smooth and revealing and yet enjoyable. Not to be confused with "laidback" as with some comments about blandness and lack of excitement. There are always other speakers that can offer a higher degree of resolution and excitement with more punch, dynamics and attack, as with some other speakers that are more colored in comparison(such as the lower range of Sonus Faber Grand Piano and Cremona) which can sound more bland and lacklustre. Bottomline most speakers sound different and comparisons are relative, and it's a matter of picking one(or a few) that suits one's listening taste and preferences.
I have not heard the Zu's so no comment there. Nevertheless, if you want a speaker that you can sit down and listen to for hours until you fall asleep on the couch this is it. The Harbeths are very smooth and revealing and yet enjoyable. Not to be confused with "laidback" as with some comments about blandness and lack of excitement. There are always other speakers that can offer a higher degree of resolution and excitement with more punch, dynamics and attack, as with some other speakers that are more colored in comparison(such as the lower range of Sonus Faber Grand Piano and Cremona) which can sound more bland and lacklustre. Bottomline most speakers sound different and comparisons are relative, and it's a matter of picking one(or a few) that suits one's listening taste and preferences.