I have a minidisk deck and portables for about 5 years, and AFAIK they always compress audio, at least with ATRAC3 for 80min, which is yet tolerable, but it's still MP3-kind of... Don't really use them anymore... IPOD might be the best, I don't know if its DAC any better then in a good portable CDPs. However, you at least eliminate poor optical reading mechanism of portables, so assuming you've done very good audio extraction, you can get some better quality.
