Glad you got it working! I think we're confusing two things. For some reason, I thought you were asking about USB host is where the phone acts like a computer and you can plug USB peripherals into it like mice and flash drives. USB Mass Storage mode for syncing means the phone emulates removable storage (flash drive or SD card for example) when connected to your PC (as opposed to connecting via MTP which is the default with Android 4). LG phones do MTP, PTP, tethering and PC Software mode (for using LG desktop software with the phone). You're right that it doesn't have mass storage mode.
Many media players use MTP, and my guess is that your car should support that. Part of the problem with the GS2 might be that Samsung had an odd way of implementing MTP for their first few phones with that profile, and they didn't play well with several things including Mac computers. Alternative ROMs might have provided a better stack.