If this goes well, you might want to consider retraining some skill ranks into Truespeak so you can take the Fiendbinder PrC, if Adrian decides he has a flair and a taste for enslaving demons to do his bidding. The flavor's appropriate, and the only thing Master Specialist has left to offer you is the Major Esoterica in 4 levels. 2 levels into Fiendbinder would only be 1 caster level lost, and you'd be able to permanently bind a Succubus to your service by using its personal truename - just like you're doing now, but with the ability to bind more demons if you want, and some other nifty perks.