I lived with the for 3 weeks on home demo and I can categorically say they need a good twist on the volume knob to get them going they are not low volume listening speakers if that's what you're after its nothing but tweeter at lower levels. If you're after a full sound at lower levels brands such as Revel, B&W, KEF Burchard audio will outperform on this front. And for non "monitoring" speakers the revels m106 performer series show them a clean pair of heels easily offering far greater sound stage and faster delivery of the music which is meant to be ATC's ace. And if your thinking because the ATCs are a sealed design you can put them up against the wall think again, they need plenty of room, not too mention some really heavyweight stands something like Partington broadsides
Think about ATC's pedigree, they're studio based monitor company but packaging to consumers, these speakers are designed to be played load for hours on end, the driver assembles make up most of the weight of the speakers the drivers are tested to extremes.
Your Yamaha seems powerfully enough, ohm spec really doesn't bother me with modern amps, it very much a guessing game with the way amps delivers the gain. The 83db spec suggests an amp that can deliver clean volume when turned up, some can't.
Putting my own views aside, For the vast majority of people, ATC is not the brand they want especially if you're not prepared to listen at full gas the whole time. ATC come into there own with there active designs id be looking at the a19scm the active version of the passive 19s you'd proably enjoys them more. A dac wth a volume control done! very clean set up.
Passive for the price id rather go JBL revel or B&W