Yes, adding a power amp to your AVR will be a huge improvement and one that you will immediately hear. The Parasound A23 will be a very good choice.
But do you need an AVR at all? If you only listen to 2 channels, then I suggest getting rid of it altogether and buying a good 2 channel integrated amp with a built-in DAC instead. Pick the right one and you won't need an external power amp either. This way you'll still get a better power amp section and the benefit of a superior preamp section as well.
Do not underestimate the importance of a good stereo preamp. The preamp sections in AVR's, even in "pure direct" mode, are a mere afterthought.
But do you need an AVR at all? If you only listen to 2 channels, then I suggest getting rid of it altogether and buying a good 2 channel integrated amp with a built-in DAC instead. Pick the right one and you won't need an external power amp either. This way you'll still get a better power amp section and the benefit of a superior preamp section as well.
Do not underestimate the importance of a good stereo preamp. The preamp sections in AVR's, even in "pure direct" mode, are a mere afterthought.