Luxman L-509X for ATC SCM 19v2/40v2, thinking integrated to start with

Did you ever find out? I agree, my ATC SCM40v2 need juice/current to sound good too. I have Hegel H360 which sounds great however due to the ATCs being inefficient I need to give it some volume for them to wake up and give me full range.

@intensemojo I got different speakers so I went with Benchmark AHB2.
You could try Coda CSiB Integrated Amplifier. Or if you are thinking separates then there are so many options starting with the very ATC P2 amplifier.

With a sensitivity of 85dB your current speakers will never sound properly alive at low volume.  That's just the nature of low-sensitivity speakers.  Been there, tried it (with an array of different amps) and failed utterly.
The only way to achieve engaging sound at low levels is to use speakers with a sensitivity of at least 90dB.  95dB would be better, 100db better still.

@agrippa, ATCs are rated as 8 Ohm, they are good with more power but I do not think they will have a problem "engaging" with a reasonable amp. I have heard Harbeth which are harder to drive and they get pretty loud. It will depend on how far you sit from them. For many of us speakers like ATC are end game. In proper room / or with correction ATC are glorious and yes with good amp. Best to go active with them. 

I’m unsure if you misunderstood me or not....

You mentioned in the OP that you " like to listen to music at low to normal levels " and I merely pointed out that in order to achieve engaging and dynamic sound at low sound levels speakers with such a low sensitivity is very much not the way to go.

I never commented on the quality of ATC speakers, which I think are very good indeed. They do however need a lot of power to open up and even then only sound their best at "normal" listening levels and up. Like every other low sensitivity design, at low volume settings they sound a bit boring and unengaging compared to speakers with high sensitivity. That is, again, just the nature of low-sensitivity speakers.