Thinking of upgrading from pass labs x250

I use my my X250 to power my infinity RS4.5s but having to move it to my main room to power Dunlavy SCIVAs.  I was using two citations IIs on them but the tubes just sound flat.  I know the pass labs will get the job done and was thinking of upgrading the pass labs during the transition.  Sure would like to get a X250.8 but a huge price difference.  For your info I use a Dude tube preamp on the front end.  I'm one of the guys that like mixing tubes on front.  Just a preference I guess.  I know the X250 is worth around $1500, maybe a little more.  So if I throw another $2000 into an upgrade what will $3500 get you used that hands down will put the X250 to shame?  I can't find anything.  I'm a guy that likes great mid-range, and detail.  So, I'm not a krell guy...  Just interested to see what others think.  By the way read about the X250.5 and many people say it is not a huge step up from the X250.....