Have i reached the limit or do i get a new preamp

I set out a few months ago to imprvove my humble system. Plan was to use my NAD c352 as a power amp and buy a preamp (under $900) to improve soundstage and dynamics. Instead i got a great deal on a b&k ref 2220 power amp in mint condition. Couldn't pass it up, and now i am using the NAD as a preamp. To my ears, a huge improvement. But the question lingers, is there a way to improve my system one last notch. I do think i am that close to squeezing everything out that i can: Cyrus 8x cd with separate power supply. Brass feet on maple block . Diamondback and hero interconnects. Tetra 120u speakers with bedrock cables and lead filled sanus stands. Pangea power cords. Great sound. But is there more with a different preamp, or do i start over at the next level (not gonna do it). Thanks in advance.