In my opinion nothing we mentioned will beat that Krell ksa-50.

You want to look on the back of your receiver for your preamp out. It will most likely have some type of jumper connecting the output to the input of your receiver. You want to pull that jumper out and connect an RCA from that output to your input of the power amp.

Remember your overall sound will be limited by the ability of the receivers preamp. Once you have your power amp if you really want to upgrade sound get a good preamp.