'Cos there is very little difference between the two. I have researched the subject on my Cayenne, which has Bose. As it turned out, the only part that
might be supplied by Burmester is the AMT tweeter (but I doubt Burmester is manufacturing drive units themselves, so Porsche might be getting those tweeters directly from the manufacturer). The rest of the components - speakers, amps are almost the same for both Bose and Burmester and are made by the same OEM manufacturer (amps are made by Harman, if I remember correctly; speakers are probably made by Bosch/Isophon, as they make most drive units for VW/Audi/Porsche).
So the whole "Burmester sounds system" or "Bose sound system" is a more marketing than anything else to me.
I would not be surprised, if both systems were developed by the exact same inhouse audio engineers and Porsche only pays for the nice Bose or Burmester logo they stick on top.
There is definately not a $5000 or what is the cost of upgrade between those systems in extra parts. More like $100-200 in OEM parts pricing. I bet Porsche managers are laughing on the way to the bank everytime someone orders the Burmester system