Although both the Dual Relief valve (DRV++) and MAP Maximizer connect to the MAP Line, they serve different purposes.
The DRV keeps you within safe Boost limits 25-27 lbs, and starts opening ~22 lbs, and in a way acts like a small blow off valve.
The MAP Maximizer also fools the MAP sensor but also lets the MAP sensor thinks that full boost has been achieved and allows you to run all the boost you need while keeping a max boost reading to the PCM.
If anyone needs more clarifications, please shoot me an email, or call. I'll gladly go over the details.