Here's my early assessment of dbpoweramp, I'm still testing it.
At the moment I give it a full 5 stars, it's awesome! I came across one minor problem that I don't yet know whether the fault lies with dbpoweramp or the car. Read on.
Firstly, the program does exactly what I wanted--that is, it lets me select any or all folders in the iTunes library and send the output into a parallel structure. It works like a backup program's folder chooser. I can grab them all with a single click at the top, and then deselect branches or single folders below that one. I can also select or unselect individual songs. Very nice.
It converts files of all different types. It downloaded an AAC plug-in at first use.
It lets me tell it where to place the output files, and in what format. I can save the output in folders for artist/album/song under any other folder. I can also include a variety of other tags such as song number, genre, year, or a couple dozen other options.
It uses all 6 cores of my AMD processor simultaneously...converting songs into mp3 format 160kbps at approx 150x!
The program estimated about 5 hours to convert 11,000 songs. I started the process at 11:00 pm and let it run overnight, so I don't know what the actual run time was. It was finished in the morning.
A handful of songs didn't correctly convert (not sure why), but it offered to try them again. This finished the stragglers off. I copied a selection of files to a Sandisk 4 GB USB drive.
Now for the problem: When playing live music where tracks run together with no pause, there was the briefest of gaps, maybe 1/10 of a second. I need to look at the files themselves to see if there is any silence embedded into the tracks. If not I'll conclude it's a limitation of the stereo. I may also try converting to Windows Media format, apparently that's also supported by the car.
Just an aside, iPods used to have the same problem...a very slight gap between tracks. They fixed it probably 5 years ago. If you have a lot of live music in your collection like I do it's an annoyance. If not you'll never notice.
I'll post another update after some more checking.