To clarify, essentially what a USB to analog cable does is just about what your soundcard does. Save yourself the extra money and just buy a $2 audio cable. If you're concerned about quality, I suggest you either buy a soundcard with optical output OR buy a USB to optical converter. The USB to analog really is just a gimmick...
As for the Sony MZR70, it still has the fat battery hump on the back. That makes it both unwieldy and larger than most other MD recorders on the market. If you're going to go for yesterday's technology, at least get the MZ-R90 for $180 and buy a decent quality cable to connect with your PC.
You can record any sound/music from just about any source using a MD recorder. Just realize that whatever the original format, the recorder converts it to MD compression before storing it onto the MD. In most cases, the compression is ATRAC. Therefore, all the lame USB ----> analog cables are useless unless you don't have a soundcard. Optical on the other hand is much better because you don't have to worry about distortion since levels are automatically adjusted.
Ugh! I'm wasting too much time on this thread. Time to do something worthwhile today...