I think asking if you will hear a big change is a very subjective question, you may or may not. In my setup I have noticed improvement using an amp, especially at higher listening levels.
If you go with a 2 channel amp 200wpc at 8ohms will probably translate to 300wpc at 4ohms.
If you do decide to buy an amp, Imho I would go with Outlaw, Adcom or one of the other quality amps to match the quality of your equipment.

A computer once beat me at chess, but it was no match for me at kick boxing.