If you pick the ATC50, I advise you to go for the active version, especially since you said you're also getting an amp. The active ATC 50 is noticeably better than the already fine passive version and you'll probably save money.
For what it's worth Gordon Holt, the founder of Stereophile purchased the active ATC 50 speaker as his last speaker choice. He told me that the active ATC 50 made the many live recordings he did sound more like the actual performance than any other speaker he ever heard.