Differences between Harbeth, Spendor, Graham, etc. ?

They only go down to about 45Hz, so don't expect them to make your bowels rumble.  They will produce truthful and tuneful bass, but if you want deep bass, you need to add a subwoofer (or 2 or more).

@big_greg 

They only go down to about 45Hz, so don't expect them to make your bowels rumble. 

Yes; Hz, not Db.My mistake. 

I believe my Silverlines were rated @ below 35 Hz. 

Paired with the right amp and DAC, the bass is pretty impressive, given the size of the drivers. I don't know if trading their bass extension for the Harbeths' mids would be an improvement. Unfortunately, I have very little flexibility in terms of potential sub locations.  

I have simultaneously owned the Spendor SP2/3R2 and the Harbeth M30.2 Anniversary for about a year. My amplifier at the time was the Audio Analogue Maestro Anniversary integrated. My take (both speakers used without grills as I found the grills to obscure some detail):

- Spendor: bigger sounding with deeper bass (as expected, given the box and midbass driver size difference), silkier and comparatively more restrained highs that I found to be somewhat better integrated with the mids, and very colorful, natural, organic, textured, lovely mids but with what seems to be a bit of a (rather wide and shallow) hole in the lower mids / upper bass. Robert Greene also mentions a more restrained 200Hz area in his review of the Spendor SP1/2R2. Bass is of the round variety, better suited for reproducing the reverberant body of a double bass than the sharply delineated start / stop of the bass in something like Kraftwerk. They need to be placed well away from the walls and the bass could also be a bit weak compared to the midrange in this case. I'm using them now with an Accuphase amplifier with its loudness button engaged and I'm getting wonderful midbass to midrange body and even quite enough low bass. The midrange is the star of the show, anyway. All in all, wonderful for acoustic music.

- Harbeth: a very refined tweeter, a bit more detailed than the Spendors', but cymbals have less body and midrange centered instruments have a bit of an overemphasis on overtones, I think, making for a less rich gamut of colors. It's a less saturated midrange, like looking at a picture that is a bit more black - white - silverly, comparatively speaking. Robert Plant's voice is too recessed on Led Zeppelin's "Immigrant Song" for example, making the whole piece less musically convincing - I suppose the "BBC dip" is more pronounced in the Harbeths' case?! Texture is a bit more emphasized, which is really nice for strings, especially in the upper bass which is a bit stronger than the rest of the frequencies, making the bass and mids better integrated than in the Spendors' case - especially nice when listening to cello music. Midrange and bass seem drier, though, and harder in a way, as if the midbass driver is made from a harder material than the better self-damping polypropylene of the Spendors (which I suppose it is). Also, the sound is smaller and the bass rolls off quite high, around 60-70 Hz I think, if listened t away from the walls. A more "sober" sound than the more extrovert, joyful Spendors. I sold them and kept the Spendors. 
 

I agree wholeheartedly with this description between these two specific models. I haven’t owned the 30.2s but have auditioned them a few times. I did own the SP2/3R2s for a few years.

A speaker that mostly splits the difference between these two models is the Stirling Broadcast SB-88. 

@stuartk 

I read the reviews on the Spendor Classic speakers and the reviews are very good. From what I can tell the Spendors sound a little warmer in the highs than the Harbeths. I agree with you that the Spendors sound like a better match for what you are looking for. Best of luck in your search.

@tjraubacher 

Thanks, Thomas. That's the impression I've gleaned as well.