Replacing the fans in your PSU is risky but possible. The problem is that 80mm fans are quite small, so have to spin fast to move enough air to cool properly. How hot is the air coming out of the PSU when you're gaming? If it's not very warm you could probably get away with using a slower (quieter) fan, they are just normal fans and usually have a 2 pin header so ignore the yellow wire of the replacement fan and match the black and red.
That said, you won't find a silent 80mm fan that moves enough air so you'd probably be better off buying a new PSU if you really are looking for quiet.
As for the CPU fan, without saying what CPU you have there is no way to advise a new heatsink - but any 60mm fan really won't be silent as it is too small.