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? 
Does your player have a USB input?   I plug a 2 TB drive of music I had into my Bluesound Vault 2i and it works great.   Perhaps you can copy your files to a stand alone portable drive.....
 I haven’t done much with trying to convert mp3 back to lossless, but I did experiment with one program a few years ago and couldn’t perceive any difference after doing the “conversion”.  My gut feeling is once you have stored the files as mp3 the missing 93% of bits that have been discarded can’t be resurrected with any algorithm.
My advice is to enjoy your new portable player streaming Amazon High Rez and listening to your mp3 files, which will probably sound pretty good on the player.  Buy a few High Rez downloads as funds allow and then re rip your CDs to FLAC when you return home.  If you keep trying to push the genie back in the bottle you will be frustrated and it will take some of the pleasure out of owning the new player 
... is there any point in using converters to get the files from mp3 to flac ...
Not really. MP3s are compressed lossy files, and data once discarded cannot later be recovered from the same file.
You cannot "convert" MP3 to FLAC - the information that was lost cannot be restored. You would be left with a lossless copy of the MP3 file with no improvement in SQ. Wait until you can get your CD's again and rip them to a lossless format: FLAC, WAV, etc..
Thanks all. What you say makes a lot of sense. Will be getting my cds back from storage in the uk soon anyway