Your amp and preamp are fine IMO. You'd have to spend a lot more change to do significantly better. I'd stick with copper wire only and look into getting another speaker. I think the Monitor speaker is decent, but I'd recommend looking into a nice British monitor like the Epos 12 or 14. They are quite smooth and can be found for a good price on this site. That change alone my offer you a more musical and less analytical result.
Rob
Rob