Mark will be sending you a new trial tune in the next bit, it will be horrible to drive, but it will answer some questions.
Ideally you use the hp turbo for getting the system going and transition boost (gear changes, part throttle stuff, ect...), So what Mark will have to work out in his tune will be just enough hp boost to get the lp coming up into its sweet spot, and then getting the vanes open and letting the lp take over. The real trick will be to get the wastegate to start opening with any excess boost after the vanes open 100%.
In it's current configuration, how much boost overall when the LP first moves the gauge at ~1psi, and then at 5psi, 10psi?
I'm curious as to the current boost curve. My guess, and it is just a guess at this point, is you will want the vanes to be open 100% about the same time as the LP makes that 7-10psi, and by 15 psi LP have the external wastegate opening.
Once you get that all tuned in, and you are starting to add fuel and make power, I would reconnect your LP internal gate and have it open off the LP signal at ~45psi (the 247 is efficient up to about 4.4pr or ~50psig). This should keep it happy. If everything is working right at that point you should be able to keep it at 45psi out of the LP and 55-60psi overall. But that is a ways down the road yet.