The replay gain values are applied as given in the tags for the RG values. The other even less standard tags are not used.
So if you normalize everything to a lower DB target to avoid any possible clipping you need to use the EQ/DSP from Symfonium to increase the volume, like with the pre amp. If you want to push the volume higher you can even do it and enable the limiter to avoid any possible clipping.
You might want to enable AutoEQ as it might surprise you too.