I'm a Marilyn Manson vet. Good luck on your quest, guys. You have a lot to look forward to with the next 3 albums.
I really like Portrait - it has some great tracks on it. Cake and Sodomy, Dope Hat, Dogma and Misery Machine are some of my favourites - it seems more of a sort of "fun" album than what comes later. Once you guys have listened to Mechanical Animals, you should definitely check out The Last Tour on Earth. The performances of Get Your Gunn, Sweet Dreams and Lunchbox are fucking fantastic...
really loud and they pack a certain oomph that isn't so apparent in the studio versions. Loads of other really good stuff on there too (I Don't Like the Drugs is amazing).
I love Nine Inch Nails. I haven't listened to them properly for a while now, but they're still my favourite band ever. One of the most energetic and powerful that I know about, especially live. And I've never found Trent Reznor's voice boring.
Reznor also more than discovered Marilyn Manson; he produced Portrait and Antichrist Superstar, and is often cited as Marilyn's "mentor." He also played some instruments on Antichrist Superstar, and co-wrote a few songs (Little Horn, Deformography and The Reflecting God).