Hi i have platinum audio bookshelf monitors that do not sound right...

What don’t you like with your current setup?   How large is your room?  What do you listen to?  How loud? 

Having to turn it 3/4 of the way is not an issue, it just means there is not as much gain than some other combos (your amp has adjustable gain).  Are the power guard lights on the amplifier coming on, which would signify clipping?   That amp should have enough power to cause the woofers in those speakers to bottom.   

If I were looking at an upgrade, I would be looking at the preamp, but from what you are saying, there is no issue, and no reason to upgrade unless you want to.