I thought you wanted 2000wrms? Those theloudest amps do not live up to their claims!
You said you didnt want the chavvy , Halfords type stuff, Theloudest is so chavvy, Halfords wont sell it!
Go for the lesser known but bigger brands.
www.talkaudio.co.uk/vbb is an awesoem forum that will help you LOADS. But dont mention the loudest over there
So you want one sub with 2000wrms?
What size you want?
I think a 2000wrms amp and sub is going to be hard on £600 budget, Would you consider second hand?
I'm going for an SPL Dynamics set up, 2 12" XTR woofers and a S1200S Amplifer, Only 1200wrms (600wrms per sub) but is within your budget and leaves £100 for cabling/deadening.