The Pono sounds VERY good. I think it has more "life" and, especially, detail than does the X5, after a week of listening to it. Maybe a bit less forgiving in the uppers with less than stellar source material, but with good source material it's really amazing in the uppers. Good strong bass, very good mids. I haven't done an a/b comparison yet, will do so at some point. But I can say that I haven't listened to the X5 since getting the Pono.
I have to assume that the 8 channel DAC will be "better." If it's better than the Pono, it will be very good indeed. I didn't expect to like the Pono, it was a gift and I thought "oh yeah, sure," but it's really won me over. Easy to use, though not much GUI on it (only an On/Start/Stop/Forward/Backward, a Volume Up and a Volume Down button, no way to turn off the display, have to let it time out - shortest is 10 seconds). Smallish touch screen, software works well. No EQ. Battery life the typical 8 or so hours.
I dumped the computer interface Pono app and now just drag and drop files onto it and the mSD. Loading files on it takes some time, but once it's loaded (the Pono itself, not the card), it responds quickly. No folder to folder, but it has gapless and some sort of replay gain though I'm not sure how well that's working. All in all, quite nice, though a weird shape.
Oh, and it accepts balanced cables, which I understand have a rather fantastic presence with this device. Apparently it's even better plugged in that way than with HO and iems or single-cable headphones. Even with a home unit. Check out the Pono thread, people like it a lot.
I will be buying an X7, especially if the sound quality is as good as I think it will be. Fiio makes quality products, and I think it has its eye on the prize with the X7.
I assume you can buy physical 24bit at some of the hi-res sites, but haven't done so myself. Check ProStudio Masters, I just got some stuff there, see if they offer it.