As others have said, if you are looking to make your show sound better, start with the FOH speakers. The Expression is not a bad sounding desk IMO.
If it is a workflow thing, then you might be looking at a different desk as the Expression is among the lowest functionality digital desks in its class.
Let us know what you end up with!
I've always liked the sound of the preamps in Soundcraft boards, they just have a certain fullness/warmth to them that Behringer/Midas/Mackie/Presonus/etc. don't have. A&H and Yamaha definitely are in the same ballpark, haven't had really any experience on the higher end stuff.