HI, I also have EX (which is really very good with a few tweaks and TLC), but not heard the K series. However I thought I’d share some info.
EX can’t really be compared to K50 which is 3 things in one - server, player and reclocker/format convertor.
The OLADRA upgrade to EX will apparently lift the EX to close to K performance, but not sure if/when that will be possible again. I have heard other owners remark that the improvement to EX is considerable.
So no doubt the K series server will be somewhat better again. The K servers are now K41 and K21 (probably best under reduced cpu load, and note it has only 1 ethernet port)
The reclocker/convertor in K50 and K22 adds some magic and appears to be the way things are starting to go (ie. high performance clocks and clever code to push AES or SPDIF to DACs, rather than USB). But that is a different ball game to what you have with the Sonore.