I don't have experience with either, but what were the issues you had with the 661? I'm just wondering so many people love them and praise them. If power is the main problem I would suggest just adding an external amp.
As for the Crown amp you linked to, the inputs on it are Balanced XLR inputs, and not your standard RCA inputs which are not balanced. It's a 2 channel amp so you would need more then 1 if you wanted to power all of your speakers, at least 3 for a 5.1 system.
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