While reading through the MFD manual I was really interested in the CD Ripping capability but also in the CF based music player.
A couple things stood out for me:
1. A CF adapter can be used. So a cheaper SD Media card (or even USB stick) with a CF adapter should work in the system
"If a commercially available CompactFlash adapter is inserted into the slot, your memory media can also be used"
2. The MP3 playback will not give accurate time information with VBR files.
but most importantly:
3. Folder levels: 8 Folders recursion levels (deep), no more than 255 folders total, and no more than 512 files (255 files max in 1 folder).
That last bit is surprising. The reader supports FAT32 filesystems, so in theory, you would be able to put a 16GB card and keep all your music collection in there, but if this is true, the file limit of 512 is quite small. There's a note that "without nav system", the file count limit is 999. I don't think there's a GT-R without NAV system though.
4. The music box (9.3GB) feature supports upwards of 2,900 songs ( i suppose there's no file count limit, just storage )
5. The CD Ripping feature of the Music Box uses MP3 encoding that only allows a user selectable 105kbps or 132kbps bitrates, which is rather low (quality) for CBR files.
