There's a 3.5mm audio-out socket above the SD card slot for external speaker or headphones. Maybe you could jury-rig your car's speakers to it and by-pass your dead head unit.
I haven't played with the media player for a while, but i think random play/shuffle function only works with composed playlists [the button consisting of 2 opposing arrows immediately above 'Source' is Shuffle]. If you don't have a manual and it's not covered in the abbreviated on-board help files you can download a PDF manual from this link:
There's certainly no problem with the unit recognising a 32GB SDHC and will even see a 64GB SDXC reformated to FAT32, but i don't know what effect large card usage has on the unit's media file storage capability. It was designed and released in a period when such large cards were not in use for such devices. If you don't have a smaller card to try, you could partition your 32GB card to ~4 Gigabyes decimal [i'd keep it just under 4,000,000,000 bytes] leaving the balance unallocated to check if it will see more than one folder/directory in a small card. In my [uncertain] memory with 7 series the MP3 files are like JPEG and GPI files, in that they can be scattered around in various folders on the unit or card, even loose in the root and the unit will find them, although the convention was to have mp3 files together in a folder named MP3. Many older dedicated MP3 players had a files number limit i recall, maximum 999 in one folder for instance. Sorry, no expert on that stuff really.
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