A long delayed update. After speaking to a bunch of other folks, including Pass' Kent and Desmond at AXPONA, I decided to go for the XP-17. I can't swing even a used XP-27, and both K and D use and prefer the XP-17 over the XP-25. While none of this means it will be the best choice in my own system, I'm hoping it points to a positive outcome. Ordered from Mark at Reno; should be here early next week.
Interestingly, Mark feels the XP-25 does something tonally, and to the better, that the newer phono pre's do not. However, he does think the XP-17 is a definite improvement over the 15. According to him no one who has made that move has returned their 17. As I'm also trying to reduce the physical footprint of my gear (another two box Pass device was not the right direction for me), I think I made the right choice, all things considered. I guess I'll see.