The Rega speakers are excellent. They definitely have something other manufacturers don't at the same price point, but I wouldn't say they're a speaker that's designed to be heard at their best when played loud as they're more of a hi-fi speaker. I wouldn't say anything other than the Arcam AV amps are going to do them justice, as many AV amps that lean to the brighter side of neutral are going to make them sound too 'toppy'.
Feel free to use an AV amp as a temporary measure, but they really do need a good quality hi-fi amplifier to get wgat they're about.