With that amp/speaker combo I doubt you'll notice much of a difference with a new turntable. It's like buying nicer china but filling with the same old slop.
If you want to improve the sound of that rig your best move would be to upgrade your speakers. They are by far the most important piece of the audio puzzle. You gotta ditch those sonys.....otherwise you're just pissing $$ away on everything behind them in the chain.