Sorry for delay - we were away walking (with the 876s) for a week.
I don't think the idea of an adjustable inner lining applies here. Yes, there is an inner lining but it is firmly attached to the outer, and yes, that is different from the 875s.
What I found was that the 876s could be worn with the laces undone. Well, up to a point, anyhow. The tongue is not loose like on older-design shoes. It is connected up the sides almost to the top. So when the laces are loose the tongue holds the shape.
In fact, most of the time I do the laces up quite loose, and the shoe just 'fits' properly. If I do the laces up tight I get a tight band across the upper part of my arch, due to the top lace holes, and that is not good for me.
I have used after-market inserts (NB Pressure Relief) in these shoes, and while they were quite comfortable, I think they take up about half a shoe size by themselves. So instead of wearing size 10 I would need size 10.5 for the same fit. Or I could go with much thinner socks than my preferred Darn Tough Vermont Full Boot Socks, but that is less likely.
I would suggest that they are worth trying out if you liked the 875s. They really are a step above the 875s in everything, imho.