Spend a good hour with a silicone butt plug. It doesn't target the prostate, but it has it's own special action. And it opens things up wide.
Then, when the Eupho takes it's turn, the sphincter is ready to quiver and and throb, sending the slim little guy in and out, tickling the prostate along the way, with subtle and exotic waves of pleasure.
Give it another hour, then diddle the nipples to guide the fun.