A slight disappointment is that the RNS 510 isn't SDHC compliant, which means that the highest capacity SD card you can use is 2GB. Considering that 16GB SD cards can be had for under £30 online, you could have significantly increased the storage capacity of the RNS 510 had it supported the SDHC standard. It also means that it's going to be a far more lengthy procedure to fill the hard disk up with music, since you'll have to do it in 2GB chunks.
The system will happily playback both MP3 and WMA files from any of its sources as long as neither is cursed with any form of DRM. Songs are organised in a basic tree file structure, which means it's not as simple to navigate your music as it would be on, say, an iPod. That said, if you take some time at the beginning to organise everything logically, you'll reap the benefit of easier navigation later.
If you still like to go old school and listen to your music from a CD, the RNS 510 has you covered too. The main head unit has a single CD/DVD player, while nestling inside the central arm rest is a six CD changer. So, you can have up to seven discs worth of music in the car as well as the hard drive and the SD card. That's got to be enough for even the longest of journeys.
You may be thinking that all those CD slots is something of an overkill, but if you choose to keep all your navigation data on DVD instead of storing it on your hard disk, the head unit CD/DVD drive won't be available to you. Hence the six disc changer will give you the ability to play CDs, while freeing up the full capacity of the internal hard drive. If you decide that you can live with the navigation data taking up space on your hard drive, and therefore don't need the six disc changer, you can spec the system without the latter, saving yourself £215.
It's not all about music either because the RNS 510 will also happily playback your DVD movie collection. I wasn't really expecting much when I loaded up The Bourne Identity, but about 20 minutes later I realised that I was watching the film and actually enjoying it. OK, so a 6.5in screen is pretty small, but viewing was surprisingly comfortable from the driver's seat. But in reality it was the sound that made the experience so immersive, with the DynAudio system creating a relatively convincing surround sound envelope.
Of course the DVD playback only works when the car is stationary, so you won't end up causing an accident while you're watching Jason Bourne hurtle through Paris instead of watching the road ahead. There was also a setting under the menus for TV, but there obviously wasn't a tuner present in the test car, while a look around the Scirocco configurator on the VW website showed no sign of a TV tuner option.
Finally, there's a 3.5mm aux input mounted in the centre console, should you wish to hook up your MP3 player. Of course you won't be able to control the player via the RNS 510, and with such a plethora of built-in options for your music on offer I can't imagine why you'd need to use this.