Don’t want to go off topic, but I might take issue with that statement. Why is it a requirement? This is a matter of personal choice related to whether one wants the extra base. Not everyone likes it, a small room or speaker positioning may already be giving you plenty, or you may be thinking of neighbours or partners. Why £3000? If you’re a bass fiend I can think of speakers above that value which would benefit from a sub.Any speaker on the market today for less than $3,000 a pair will require a subwoofer