As of right now I have 3 Definitive Technology SM55 Bookshelf speakers for my center, left and right. Definitive Technology SR9040 surround and Pro Monitor 1000s for my top middle speakers. I have a Denon X1400H Receiver. For the Sub I have a HSU VTF3-MK5. I was just wondering what you guys would choose to upgrade first. I know the Sub does not need to be upgraded next. I was thinking it would be the Center channel or the Receiver. I don't know how much of a change I would notice with the receiver upgrade though.\nPlease let me know any ideas you have and thanks for any help!