What's the difference between a Pass Labs X250.8 and the X260.8 mono's?

I recently replaced a legacy Krell FPB 400cx and bought a PL X250.8 to drive my Sophia 2’s. It’s a huge improvement, and I love everything about the new Pass amp except the impact/bottom end control. It’s OK, just a little polite (I know, those old FPB’s kind of set the bar). 

I play loud, so need power (I get the meters to twitch pretty often), and at the same time love the way the 250.8 presents such sweet mids and highs. I don’t want to give that up, which is what I’m told will happen if I switch to the big 350.8. Mark at Reno Hifi is recommending I change it out for the X260.8 monoblocks to keep what I like and get more of what I want. I trust him, but would like other opinions.

Has anyone heard both of these amps? Will I get more bass authority without giving up that gorgeous midrange / high end? It will be about a $5K bump including a new stand to stack the mono’s vertically with proper spacing (I can’t position them one on each side or in the middle), so there would need to be an improvement to make the change.

(CDP is an ARC CD8 and the preamp is an ARC Ref 5se)

Thanks!