From what I've read on forums, sub £2k AV receivers are usually used. I believe this is done to show that they can be used with budget amplification, and don't need expensive amplification to drive them. Although this is true of most speakers anyway, speakers at the level of KK/MK should really be used with pre/power setups in order to provide the speakers with more capable amplification, allowing them to be demonstrated at their best - when people audition products that have received a large amount of hype, they want to know exactly what they're capable of. High quality speakers using high quality drive units will respond very well to better quality amplification. As it stands, if these products can't be auditioned with suitable partnering electronics, no one knows what they're capable of, or even if they are capable for that matter. I've used my Quattros with an Anthem MRX710, and they sounded great, but not as great as when they're used with a good quality dedicated power amplifier.
It isn't out of the realms of possibility that the Quattros could well give the S300s a serious run for their money - both have their advantages and disadvantages in comparison to each other.