Recommend contacting your local owners club to see if at the next coffee gathering there will be cars with any or all of the following 4 options: base audio, base audio with Reus, premium audio, and premium audio with Reus.
Bring the best FLAC or similar files you can lay hands upon (of music with which you are already familiar) via a USB stick and go to town. I'd recommend melodishop.com or hdtracks.com for the FLAC files if you haven't any handy. There's FLAC and there's FLAC, but for a quick listen, any FLAC will do.
Anecdotally, I found there to be more midrange in the premium audio package versus the base audio package. Beyond that, any Reus upgrade will make either sound better, via, in part, the addition of an active center channel, and amp/subwoofer combinations. In the end, I went with the base audio and a Reus upgrade, which is to say the $2,500 for premium audio went towad the Reus instead. The thing with Reus is that once you buy the package, you're done - they'll transfer it from car to car for the cost of labor. Just something to keep in mind.