Thanks to Vincent and Connersw.
That helps.
It is very confusing to the relatively uninitiated as this would mean (in real world terms)...
All mp3's will effectively be presented as 44.1, therefore the option in JRiver MC for 'Less than 44,100 Hz' is 'mostly' redundant?
I previously thought this would have allowed me to leave poorly encoded (128, 192 etc) mp3's untouched and pass straight through.
Upon hindsight this makes no sense as how would my DAC know what to do with it (aside from lowest common denominator?)
So to recap,
all CD's or CD based media rips (mp3 regardless of bitrate, all flac, or wav ripped from CD, etc) will always be 44,100?
I initially hated (very) the overly complex nature of Media Center 19 (I am an IT manager in a school so not frightened by software or hardware setups from 'scratch') but the feature that kept me going is the IOS remote (much nicer that the overly feature rich windows based interpretation) and having my ipad/iphone as an actual media device to listen on was a bonus.
I am migrating away from my Sonos investments due to their refusal to accept change and support above 48.
Are JRiver going to consider adopting the 'Wizard' setup idea in future for those who are getting confused - eg Myself?
There are so many options and functions (having to enable DNLA was not the most obvious either!)
Once again, thanks for the answers.
Arthur.