"what will happen if i upgrade my PRE ... i want to still be able to use those audio controls ... "
if your "pre" accepts external control adaptor .. yes. or maybe pre out goes into external volume and from there goes to power amp or speakers. then yr external adaptor should accept universal pre outs.
about sound qaulity it goes down a bit as more electronics one add in audio or video electronic current path.
(the shortest current path is the best path)