Torn Between Two AVRs
Mark Fleischmann, HT's primary audio reviewer, has this to say in response to your question:
"If your room has any gross acoustic flaws that can't be fixed with an equalized sub alone, then Anthem is the better choice. Arcam's room correction is rudimentary, and even the instruction manual recommends that you get along without it if possible. On the other hand, for sheer sound quality, Arcam is unbeatable. If possible, step up to the AVR600 (also among HT's Top Picks reviewed here) to get the benefit of rail-switching amplification, which switches between different output transistors depending on the demands of the signal, allowing the amp to provide more power into lower impedances with greater efficiency and less heat."
Keep in mind that the price jump from the AVR400 to the AVR600 is a big onefrom $2500 to nearly $5000. Whether or not you can swing that, I'd go with Mark's advice in any case.
If you have an A/V question, please send it to firstname.lastname@example.org.