dedicated preamp.

I don't think it would make any difference since you are staying with a YBA preamp ! I think if you call YBA they will tell you the same !

You really think they would tell him that there's no improvement in sound quality as he moves up the YBA line? Why build them if that's the case?

Just remember that when one is finely tuned regarding what they are listening to, as is commonly the case in these parts, any change might require other subsequent tweaks in order to get things tuned in properly, like changes in speaker location/orientation in order to get the soundstage right with a different amp. So a change for the better in gear might not result in a clear overall better sound initially, but that should prove to be the case eventually once everything is tuned in again properly.

I would certainly think that the YBA preamp that is the same price as the YBA integrated, would be better as a preamp, and also retain the sound you have now...

I think you should try a dedicated pre just to see if it betters your current set up. I think you might like it better, in spite of the all YBA of it all.