Sorry, I didn't see this post until now!
Both of those receivers are very good; make that excellent but are good for diffferent things. The Onk has a much more "up-front" sound which makes it more exciting but the timing isn't as good (that is the ability for the amp to stop and start with the music.) The Arcam isn't as exciting and isn't as powerful, but it is better at music.
My choice? The Onk, because I think it looks nicer and I prefer an exciting listen, but the Arcam is equally as good and is built much better.