You’re not gonna get any useful recommendations here due to the little info you’ve provided about your specific equipment, room, and sound preferences. Put a little more effort into providing this critical info and you will get something useful here.
Will there be a dramatic difference?
I currently am running my Thiel CS 7 speakers on a 25 year old Carver amp I have an amazing Audible Illusions modulus phono preamp. It all sounds pretty incredible. I am considering Parasound a 21 and I’m wondering if that upgrade will make a dramatic difference in the way my system sounds overall? Would it definitely be worth the investment?