Zu or Harbeth

I have heard both also (at shows), and the 40.1's are the ones between the two that had me trying to figure a way to get them into my listening room. One of the nicest sounding/presenting speakers I've heard to date. Not neutral/uncolored, however. But the coloration is purposeful within the design, like the resonance in a guitar.
I am a neutral junkie, so I stayed in the Harbeth room long enough to be pretty sure that I wouldn't get fatigued by these speakers. If anything, they evoked that addictive quality we look for.
Better with accoustic music; but a good overall speaker (not just monitor) IMHO.

I think you'd love the 40.1's... I sure do. I can't speak to the sound of the Zu's, as I have never heard them, however, while I like that they are very efficient, I am turned off by the way they look (I know many would say the same about the 1970's retro look of Harbeth). Your room size would be great for the 40.1's... and I think your decor would also blend well with the Harbeth's.

When I heard the Harbeth's, I found the sound to be non-fatguing, but a bit bland. They were driven by a Naim amplifier (I can't recall the model), and they were also driven by a Leben CS600, which I brought along.

A speaker that I find somewhat similar with a British sound, but with more jump and "juiciness" is the Audio Note AN-E.

Many people love the Harbeth sound, but I think it's a speaker you should hear before you buy (as is the Definition). From a resale standpoint, I believe the Harbeth would offer a better return at this particular time.

I haven't heard any of the Zu's, but I love the Harbeth 40 (haven't heard the 40.1) and I would buy them in a second if I had the means. Speakers are always an individual choice, but try to hear them before you make a decision.

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.