Welcome to Rennteam!

In answer to your question I wouldn't go for the second option under any circumstances if it has had a hard early few miles as a demonstrator.

I've had my Boxster S 5 months now and done over 5,000 miles, so I can advise you with the benefit of my experience.

The black car sounds ideal, I've got Bose in my car and I don't actually listen to it that often, the engine sounds much better. I've also got PCM + navigation and with hindsight I would have been better buying one of the portable units. Here in the UK TomTom Go seems to be the best, but I guess you've got equivalent kit in Taiwan. I've also got 19" Carrera S wheels, and whilst they add visual drama they don't add anything to the driving experience and some here say the 19" wheels detract from ride and handling slightly. You don't really need power seats (they add weight) and with no PCM you wouldn't miss the multifunction wheel (I went for the sports wheel). Other options line stainless steel exhaust (would look great with black) etc you can always add with no problem if you want them.

Black with sand beige is a distinctive and classy combination, personally I'd rather have that than GT silver with grey as you don't have much colour contrast with that, but of course colour choice is down to personal preference.