Std S3 brakes are 'ok' but your definition of 'crap' needs a little more info to be able to understand the context as even LCR brakes are 'crap' depending on how you use them and what pads/fluid you use...
Before I changed to 4 pot calipers I used Motul RBF660 fluid and Ferodo DS2500 pads on A N Other discs and the brakes were night and day transformed... having 4 pot calipers with std pads and fluid may feel better initially but if you are a 'user of brakes' then they will soon go off like std brakes and you are no better off...
As said, second hand LCR setups can be had for 400-500 quid, new/decent (I mean Brembo/AP Racing based kits) are a grand or more... there is a massive brake thread in the FAQ sticky at the top of this section... if you are on a budget then fit DS2500 pads, replace the fluid with Motul RBF 600 or 660 and just fit std pads/discs to the rear as they do no work anyway...
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