@cundare2 I was not going to comment because you asked for an integrated. However, since you are open to the Benchmark stack, I was also going to say that would work nicely with the Harbeth’s.
I hear the Harbeths as a bit warm and the Benchmark gear is as neutral as can get. On a warm speaker the synergy could be good. I have a warmish Yamaha NS5000 speaker, and I got the Benchmark AHB2 to try with it. I really wanted to make it work because I like the AHB2 sound. However, I found my CODA #16 better. Surprisingly the bass on a single AHB2 was as good as the CODA #16 (a bass monster) on my speakers. That is not the case with the AHB2 and other more demanding speakers.
I use my Benchmark DAC3B stacked on top of my Benchmark LA4 preamp. The form factor is smaller than most integrated amps. On my warmish speakers this is a winning combination. On a less warm speaker I would change the DAC, but I would use it with the Harbeth.
For your Harbeths, a pair of mono AHB2’s would be the better choice over the single stereo. I am putting mine up for sale later today. However, Benchmark will offer you a 30-day home trial, which is a better choice than buying a used unit blind.
The Hegel 390 is the integrated I would look at pairing with the Harbeth, though the Benchmark DAC3B and LA4 pre are better to my ears. Smaller form factor than the Hegel. You can safely stack all 3 Benchmark components,