I own the 510, have owned an older Arcam AVR200 and NAD separates. I'm no audiophile, but I've found the MRX to be excellent with two channel music. Is it audiophile quality? Probably not, but I know of few people who really know what that means, including me. IMHO AV receivers are more interested in bells and whistles than overall sound quality, and audiophile equipment tends to be a diminishing return against cost. Anthem takes a different tack, with emphasis on sq, less so on bells and whistles, and with Arc 1m they have made me a true believer in their version of room correction software.
I'm still in my honeymoon period with this receiver after a year, which is unusual for me. I no longer experience the listener fatigue I used to, though the rest of my system has not changed. To be honest, I have used it primarily as a preamp, and it has not been problem free, with a low volume oscillating hum from the preamp outputs. I am currently waiting for a replacement. Anthem product support has been exemplary. I have however listened to it extensively without outboard amplification, and find it excellent in its own right, with plenty of power to run my relatively inefficient all Vandersteen set up. The Anthem definitely doesn't skimp on output.
One caveat, which is why I prefer an outboard amp, is that the receiver utilizes active cooling....with a fan that is far from silent. When running 5 channels at somewhat exuberant levels, the fan is truly noisier than I think is acceptable for an audio component. As a preamp...not an issue, in two channel mode I seriously doubt the fan would ever be evident. Speaker efficiency and resistance, room size etc. are obviously contributing factors, and your experience could easily differ.
BTW. The previous Anthem series utilizes the same amp section as the current models, so liamgdr's experience applies with the new series as well. Build quality is excellent, and the ARC implementation is very straight forward and flexible, with lots of user control. Bass integration if you utilize a sub is phenomenal. Arc 1m doesn't "juice up" the sound as much as just makes music and movies sound balanced and less muddled. Dialog is excellent for movies, always a weakness with the Arcam. Don't know how to describe it. Usually I can find some sonic defect that bugs me...with the Anthem, there just isn't anything to harp about. I think you'll be pleasantly surprised. Not that I'm planning on replacing it anytime soon, but based on my current experience, I'll definitely take a long look at what Anthem has to offer the next go around.