....take a hard disk's worth of music in my car
Pre production units have been in the hands of volunteer testers for two months now. We are just waiting to hear from the factory for precise delivery dates for the mass production units.
The brennan will import music files with type wav, flac, mp3 or m4a.
If the portable Brennan has a low capacity internal SD card, one strategy could be to use it only for the operating system and store all music on a low profile USB drive, like THIS. The USB drive could be removed and connected to a B2 to refresh the music library.
The easiest way to transfer music is to plug your B2/JB7 backup disk into BB1 and use the Browse USB function. In fact BB1 will play the music directly from the backup disk - so there is no need to transfer.
....recommend using USB out to an external DAC/headphone amp.
USB DAC/Headphone amp testing

Haven't tested yet