Depends on how the calculator wants you to enter the dome/dish volume. The one I used says dome volume is entered as a positive and a dish or valve relief volume is entered as a negative number. Since it has already been stated the pistons are flat tops and virtually all perfromance flat tops have a valve relief its pretty easy to conclude the "Dome volume -7.5cc" is referring to the valve relief volume so you enter the number as your calculator instructs. Even if it doesn't tell you you can think it through and realize that a valve relief or dish adds chamber volume which lowers compression and if one way gives a lower number than the other you can conclude its the way that gies the lower number.
As far as compression ratio goes the "some say ....." is a useless statement, there are too many other factors that come into pay when trying to determine the how much compression you can have. With all other things being equal aluminum will allow for a higher compression ratio because it will transfer heat away from the combustion chamber faster. This comes at the cost of less potential power, with all things being equal, including compression ratio an alumium headed engine will make less power than an iron.
FWIW, I have a 360 with 10.6:1 compression with a small cam than has been mentioned here and it runs with no detonation just fine on 89 octane and it I am careful about not loading the engine in the lower rpm ranges it will run on 87 octane without detonation. I get away with this with zero deck flat top pistons and closed chamber magnum heads with a tight 0.040" quench distance. I have a Comp XE268H cam which gives me a cranking pressure of 195+/-5 psi. From a reliability stand point I have put almost 46,000 miles on it since July 05 when I installed it and I do not baby it.
When it comes to Octane Boost when the bottles advertise that they raise the octane "4 points" what they really mean is it will raise 87 to 87.4 (neat little marketing ploy, they haven't lied but they sure make you think a bottle will turn 87 into 91). So, if you have a detonation problem it's not likely that its going to make much difference.