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You will not get an Anthem for that.
What M&K speakers do you have? From what I know they tend to be lower impedance than typical home AV speakers and need good amplification to get the best from them. Hence I would suggest your budget is way too low. About the best you will get for your budget is the Yamaha 1073 which is £500 (used to sell for £1k) but even this may not be as good as your current receiver.
I think there is an MRX300 available for £499 at the movie rooms it is s/h but does have some warranty.There are also Onkyo 818/628's about for £499/599 both these brands go well with MK's. Which MK's do you have?.