Where to go from XP-15? XP-17? XP-25?

I've been happy with the XP-15 for a number of years - first supporting my modded AR ES-1, then a VPI Classic 3, and now my Avenger (my final stop, I hope). I love the fine adjustability of MC loading and the gain which will support running carts down to about .2 mV. But with the Avenger I think I've reached a point where I should consider a move, in part because everything I find about the XP-25 seems to indicate it is far and away an improvement over the XP-15. With the inclusion of the XP-17, however, I'm now a little hesitant.

I run two arms on the Avenger, so it might suggest going to the XP-25 is an easy decision, plus the well regarded sound quality (I've heard the 25 a number of times, but not in my own system). OTOH the XP-17 is based on some of the same technology that's in the XP-25, plus it's a one box solution (I kind of like that). The questions out there for anyone who can help - has anyone been able to compare the XP-17 to the XP-25? How do they sound compared to each other? Would the XP-17 be considered a step up or at least equal to the XP-25? If the XP-17 is generally considered a must try next to the 25, I can always run it face into the rack and keep the back end exposed for tonearm and loading changes (not pretty, but effective).

I'm also a little concerned about any change in sound from the previous generation Pass gear to the new (12, 22, 17, 27). I've read, for example, multiple views back and forth between the .5 and .8 series amps, a few saying Pass' reduction in negative feedback and modification to the second harmonic character in the .8 are not to their liking. I hadn't heard if there's been such a (perceived) change in the small signal Pass devices.
Dear @tonyptony : Pass devices/items are a guarantee of high quality level performance, designs and excecution to those designs.

The answer with out doubt is to go a head for the two box XP-25. The 17 has no single advantage over the 25 other than a lower price.

Regards and enjoy the MUSIC NOT DISTORTIONS,
I owned the xp-25 for 5 years.  Excellent phono stage.   I have also heard the xp-15 im my system and the xp-25 is a step above in sound quality.
  Have not heard the xp-17 .
Raul, have you had a chance to hear the 17 by comparison? There's no doubt in my mind the XP-25 is better than my 15, but I haven't gotten a clear sense of the 17 yet. 
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Yes, Mark has helped me over the years with my current Pass gear. I'll have to give him a call, but it's always good to try and get additional thoughts from folks who've had an opportunity to hear this stuff. 
From what I've been able gather, the main improvement of the XP-27 are dual mono power supplies that improve the already excellent noise rejection of the XP-25.  I'm happy with my XP-25, the more so after replacing the stock loading resistors, coupling caps, and input RCAs with better pieces.
@dgarretson , please do tell. What did you do there?
Replaced the loading resistors, which are clearly labeled, with Texas Components TX2575 nude resistors, and replaced the stock electrolytic and MKP coupling caps with ClarityCap 4.7uf CMR.  Replaced the stock Cardas RCAs with Bocchino Tomahawks and WBT Next Gen. Next step is to try a Less Loss 64x firewall in the power supply.  No reason that I can see to abandon the XP-25. 
It appears that Pass could've used better quality parts, unless you modify sound to your liking which might not be to everyone's.
@inna All products are built to cost. Improvements are always available, whether through trade-in or thoughtful modification.
Bocchino Tomahawks

Well, that's a new one for me. I've never heard of these. What are they? Also, did you do all this work yourself? If so, was any of it exceptionally difficult? I do have some ability in doing circuit work up to an including SMT devices.

I did it myself. You need good soldering and desoldering skills.  The Pass unit is easily disassembled. There is space for the larger coupling caps mounted on perf board raised above a small section of the main PCB. The Bocchino RCAs are solderless with compression fittings and heavy silver plating over solid copper base metal. Just remember that you will void the warranty, and if it ever needs service, Pass’s formal policy is to first return the unit to stock condition. I doubt they would care about the resistor and RCA changes, but you might have to reinstall the stock coupling caps.

PM for details and photos if you decide go for an XP-25.

Thanks. I'll let you know what happens after I talk with Mark.
I assume that you're thinking of a used XP-25?  If you're buying new, definitely go for the XP-27.  You can always do the same mods to that should you feel the urge. 
Yes, used. I can’t swing a new XP-27! :-) But I’m still trying to see if there’s anyone out there with firsthand experience comparing the 25 to the 17. 
Whichever you go for, add a Less Loss 64x Firewall to your Xmas list.  I spent the afternoon juggling three of these through the system.  Of six components evaluated with the 64x, the XP-25 benefitted most.

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.

Curious- what if anything have you learned are the benefits of an XP-17 over the XP-15? An XP-15 owner here is curious- 

While I very much like my XP-15 . . . but, you know- 
Well, when I spoke to Kent he said the new 17 and 27 have improved power and also lower noise (with of course the 27 being better still). Mark at Reno says I should expect a blacker background and improved dynamics. As I use some low output carts including an A95, I figured it might be a good step to take for me. 

I like the dynamics of my XP-15 but I do think the noise floor could be lower, but then again I am using fairly high gain, as I have a low output MC cart

The folks at Pass and Mark at Reno have always been super helpful to me-
Agreed. I've been very pleased with the support I've gotten from both the Pass gang and Mark. 
I have the highest respect for Nelson Pass and his products, but it seems to me that at this stage of the game (in reference to the evolution of solid state audio devices), any decent SS phono stage should already be "dead quiet", which is to say, not noticeably a source of added noise, even at the highest gain settings.  Even my Manley Steelhead, which is a hybrid design, fits that description.  So, I often wonder at the endless claims of "blacker backgrounds" and etc.  SQ can always get better or evolve to be more suited to the taste of a particular listener, but S/N ought already be very very good for high end solid state devices.  
You make a thoughtful point, lewm. I guess I'll see what happens once the 17 gets here. 
The answer with out doubt is to go a head for the two box XP-25. The 17 has no advantage over the 25 other than a lower price.
And that couldn't possibly be a consideration, could it?