If you insist on changing the amp only, to get a worthy noticeable improvement you will need to step up to a Ayre VX-R ( even better a VXR twenty), or a Luxman M-700u / 900u.
And still if it was my move I would change your preamp also, because each night you will go to bed or listen to your system you will ask yourself ( little inside voice) how better would your new amp sound with the latest and better preamp like a KX-R or a Luxman C900u, ARC Ref6. ( this is why I was giving you the advice of getting an integrated like the Luxman L509x wich has one recent hugely good preamp section built in).
And still if it was my move I would change your preamp also, because each night you will go to bed or listen to your system you will ask yourself ( little inside voice) how better would your new amp sound with the latest and better preamp like a KX-R or a Luxman C900u, ARC Ref6. ( this is why I was giving you the advice of getting an integrated like the Luxman L509x wich has one recent hugely good preamp section built in).

