Recently purchased an integrated amp for my Harbeth super HL5+XDs as well.
A Modwright KWH 225i, which has tubes in the pre-amp section. Bought it online used (1yo) and paid half price. Otherwise, I’d never have been able to afford it.
I spent a lot of time researching units for these speakers, and what I discovered is that pretty much anything will pair with them. More important is to buy an integrated amp that doesn’t have anything you don’t need.
I was looking for something that was just a pre-amp and amp — because I don’t want to pay for things I don’t need — and that’s all the Modwright is (not even a headphone jack). I ended up buying a unit that had the optional phono preamp. Didn’t need it, even though it’s better than the one I had, but that unit ended up being cheaper than another used unit that didn’t have it.
Also, the guy I bought from threw in a pair of $300 tubes as well.
I was also wary of buying something with an overseas markup of some sort (I also bought my Harbeths used for almost half price). And Modwright is made in, I believe, California. (Unsure where you’re based)
Also I like less well-known brands (sometimes) because (sometimes) I feel like part of what you’re paying for is a brand name.
There are a lot of other smaller players out there you might like, though the smaller the player sometimes the greater the cost.
But going the other direction, another name to consider that might fit a slightly expanded budget is Naim. The Naim Supernait 3 gets a lot of good press for working well with Harbeths.