Hi,
Unfortunately the top comparison linked to sells the LCR-850s rather short on the amplification side of things Imo!
(I didn't get too far in the other link as I took fright at reading 14 pages

)
My experience with M&Ks is that if you used an all in one reciever you usually got a comparatively lack luster performance as a result,
Changing over to a good quality standalone power amp really made a noticable difference for the better.
It's one of the real flaws of the M&Ks really!
However your own amplification is perfectly fine and I'd wager would get a different result because of it!
If you generally like the sound you get from your M&Ks and their relatively small size then an upgrade to the models mentioned above should provide a very nice step up, while at the same time keeping the sound well matched with your rears.
Where the Xtz's provide incentive is when bought 2nd hand they do seem to represent good value with some relatively cheap deals cropping up,
(M&K's with their almost cult following still seem to demand higher prices by comparison).
So I'd say if you fancy entertaining a change of makes and possibly freeing up some cash in the process then give the Xtz's a bash! Don't let the ports put you off, they can always be bunged if close to the wall & if you don't like the result you can always sell them again and move further along the M&K route.
Paul.