Harbeth - Audio Research?

the audio research and harbeths will go well.
Go for the SHL5s although the M30s are also quite nice.
The Harbeths for that matter will go with most amps.

You know, the thing is, I really love the Harbeths but if you haven't heard a lot of comparisons then your upgrade bug talks to you. "Wonder how those Thiels would sound" "Wonder how those B@W's would sound" It's definately an affliction!!!!! Wish there was a speaker borrowing company like the cable company.

any product that makes one listen more is worthy

The Harbeth is more "natural" and "musical" and will be enjoyable on a wider range of recrodings. You don't find many Harbeth owners unhappy with their speakers. I would love to have a room big enough for the M40s, but the HL5s are proabably perfect for most normal size rooms (12x18 or 20). Will you loose out? Doubtful you'll feel that way - though the HL5 proabably don't go as deep as the Thiel. A more "musical" and "natural" option while maintaining the phase coherency and time alignment you are use to (these type of speakers seem to soundstage differently) are a pair of the Vandersteen 3A Sig, which will indeed be as full-range as what you are accustomed to, and very frequyently matched up with 100 watt Audio Research amps. Add a pair of 2Wq subwoofers and you have one hell of a good speaker system.

I was having a problem similar to yours (reported in other threads)...I was using Vandersteen 3A sigs, which are very nice speakers, but they tell you everything that is wrong with the recording, and I just became terribly fatigued by it. I bought some Harbeth M30's and was greatly relieved. The midrange was much richer than the Vandersteens, which, because I listen to a fair bit of classical music, was quite wonderful. And voices...uhmm, very lovely. However, they are monitor speakers, and are, themselves fairly revealing. I eventually switched to Compact 7's, which are probably a bit more pleasant all around--BUT, I would read the series of reviews of 4 of the Harbeth speakers by Paul Szabady w/ Stereo Times online. In the end, he preferred the HL5, and I think that's probably the way to go.

As it happens, I used an ARC VT100 mkiii with both pairs of Harbeths. It was a fine combination.

As always, if you can try beforehand, do. But I think it is rather rare that someone doesn't like the HL5's. I should add that, with the M30's and the C7's, I concluded that I liked having a modest subwoofer. (I just use a single Essex.) I don't think you'd need that with the HL5's