Hi Metaldetektor,
I had to think about your question a little. I'm not sure that I would describe the SONs as papery. I do think that they are very good at representing the detail and harmonics associated with lower lower frequency instruments. For example, bass drums have a lot of detailed sounds generated from the materials the drum is made from. I don't hear that from more "clean frequencies" such as electronic instruments (eg. synthesizer). Again, i'm guessing the precision afforded by the field coil driver technology has much to do with that outcome.
In terms of quirks, I don't any real true deficiencies to speak of. I would say the characteristics of the SONs that you would need to decide if they are to your liking are that the presentation is centered or possibly even a little set back. So if you're wanting a very forward or outfront soundstage you won't get that. Don't read "set back" into that though. Second, the detail is not overemphasized. Grannyring said it better than I above in that they are wonderfully resolving but utterly smooth. It is easy to listen to for a long time vs many speakers that tire out my ears after a while. The AMT tweeter is outstanding in that I think it is primarily responsible for this resolving yet smooth result which is pretty rare in my experience.
The setup is interesting. I find they are fairy generous in providing a good image if you have a people listening off center. Much more so than my previous Reference 3a's. But they are also very particular when find that last 5% of perfection in setup. I notice very small tweaks to toe in and position. I've got my chair about 8 ft away and front baffles about 2.5 - 3 ft from the front wall. I ended up putting the AMTs on the outer most position as it allowed me to move the cabinets a little closer together. This was done to move them a little further from the side walls which sounded more linear in my room. The flippable tweeter is a unique setup feature that can you don't have with most speakers.
One more interesting note. The speakers are not tall so you'd think it creates primarily a shorter soundstage. I think it is possibly a littler shorter than my previous speakers that were probably a foot taller. However, it produces much more variation in soundstage height than other speakers i've spent time with. I can only assume its more accurately representing the recording given the height variance. Some recordings sound quite tall vs others.
Hope this helps but let me know if you've got other questions.