Options for converting CD rips

Hi all 

First time poster, nice to be part of these forums. Looking for some advice. Just about to receive delivery of a hi-res audio player. I use Amazon music HD but have 21000 tracks previously converted from my CDs. I would rip them again but I am living overseas and my cd’s are in storage in the Uk. Not prepared to pay out and download hi-res versions due to cost so is there any point in using converters to get the files from mp3 to flac or I should just wait to get my cds again? I suppose if the conversion is easy enough with some of the programs I’ve researched then it’s no harm and I will see a small improvement in quality then it’s worth it but will the gains be really minimal? 
Cheers
chris