The best way to future-proof: Own, don't rent. Buy used CDs on Amazon or eBay, rip them to a lossless format, and resell them. Sure, this eats more hard-drive space, but that's cheap. Then just make lossy files in the best format your current portable player supports. Alternatively, rip to MP3 at a high bit rate (320 kbps), and store those discs in your Mom's attic.