The recommendation is 30w to 120w. To put it in perspective a 30w amp would output 96.1dB at maximum. That will cause hearing damage between 3 & 4 hours of exposure. Now that would be max output and you would never want to run at max so a nice 40w to 50w amp will do a lovely job of driving those speakers comfortably.

I personally like the Rega Brio R very much. I think it offers an amazing level of detail and quality bass at its price point largely because it has very, very few features. It is $950 and it is comes highly recommended from both Stereophile & WhatHifi. Full disclosure, I own one and have it powering a less efficient pair of Revel Performa3's and love it. Really, really love it. It delivers a big, very clear sound.

Alternatively, at a lower price point the MusicHall A15.3 is a darn nice amp. It is $550 and delivers big on sound quality. I like the Rega better, but lots of people disagree. It is an A+ integrated as well and it is personal preference as to which you like better.

NAD makes lovely sounding, warm integrates. They usually get dinged a bit for the bass being slightly muddy so this might not be your first choice. I think the Marantz would be a good choice though I would not choose it over either the MusicHall or the Rega.

Are you using a subwoofer with it? If so, that has a huge impact on bass clarity and if you already own one, connectivity is a concern with the Rega. If you are going to add one, your universe of choices are a bit smaller but are what would probably be recommended anyway.

Get the Music Hall 15.3 amplifier.

It is only $550 and a steal for that price.