Which Firmware is the W800i having?
In my opinion everything depends on the firmware version. And K750i and W800i seems to be on the same hardware. On several forums it's described how to "upgrade" K750i to W800i (see http://www.davinciteam.com/ and other related sites searching for K750i and firmware). The newest firmware seems not to work correctly.
What do you mean with your martin System. Is this compatible with the bmw snap in system or is this system a "free cabled" hardware?
Are you sure that your awaiting system will work. Did you have any experience.
I buy a expensive radio & nav system, a new handy and a correct snap in. This money might have been better investet in an other system.