iTiunes Music Files

I always (last decade) let iTunes make a copy of my CDs as I acquired them and now have some 675 or so albums on PC in whatever format iTunes did that in.  ....   MP3 maybe??
I made a copy of those to an XDHC card and inserted it in the slot provided in the car and can play any of that music there.  I recently bought a Cambridge CXN (V2) Streamer which also has a USB input which will or can hold a card reader or even a small SSD hard drive.  The Cambridge will be connected to my main audio system primarily for internet radio but since it can (I believe) play those audio files is there anything I can easily do to convert them to a better format before doing the copy and paste to the new memory card?  Any software required?  It's a PC on Win 10.

Thanks in advance.
If your files are all MP3s then you are stuck with an inferior format! Can't make a silk purse out of ... !
When you insert a CD into a drive attached to the computer in order to rip it to iTunes and choose "Import CD" you immediately get a dropdown menu that lets you choose the format, AAC, AIFF (the format that's on the CD), Apple Lossless, MP3 or WAV. So the files on your drive or XDHC card will be in whatever format you chose when you copied them. The default is AIFF, which is a lossless format, so if you didn't change that you should have full resolution AIFF files.

You should be able to see the file type of any file in your Music folder by following the instructions here. The file type will be the letters following the period after the file name. If it's an mp3 file it will be 'mp3, if it's AIFF it will be .aiff.

One more comment on your last question. You wouldn't gain anything by converting mp3 files to a higher resolution format like AIFF or WAV. The data was lost in the conversion process in the interest of a having a file that takes up less storage space and less bandwidth to transmit. If you did that conversion you'd have a file that is bigger but doesn't sound any better. So, first thing to do is find out what kind of files you have.