Laurie, I think you’ll be fine with the deep chocolate passion. Don’t worry about syruping, it is a sponge-type cake and has a springy texture that can handle it. As long as you follow directions, it won’t get mushy. I think I’m in the minority about this, but I don’t really enjoy a syruped butter cake (except for the golden lemon almond, I love that with syrup). However, I do like the deep chocolate passion with syrup, completely yummy. And it’ll be great to add this cake to your repetoire, it really does offer a different taste and texture than a butter cake.
As for the ganache undercoat, if you want it for taste reasons or to provide a super-smooth canvas upon which place the final coat, that’s fine, but I don’t think this cake needs it. Plus, you’ll probably want to have the white chocolate layer a tad thicker to provide coverage over the dark cake, and a layer of ganache might be getting into too-much-frosting territory.
When you’re syruping, you can spread a little of the syrup around so that it seals and coats the edges, kind of double-duty syrup/crumb coat. Then chill before frosting with the white chocolate.
Please post a picture, it sounds just lovely!