WilsonTurner said
You're dealing with magic. That means necromancy, neuromancy, etc., which means they could, because it's magic, go in to someone's mind and manipulate it at will. To kill oneself would be the only way to truly keep the information out of their hands- only willpower could delay neuromancy.
One might need to have a detailed understanding of the other species thought patterns. Same reason translation magic and the sort isn't always going to work (though translation magic and technobabble is excusable as most people don't want to spend 12 pages playing alien charades with new contacts), having evolved light years apart, the brain is almost certainly structured in an entire different way, the species will have separate instincts, mental disorders, mental triggers. While some basic things will remain the same, cognition is something we don't even understand properly in humans. With aliens, we'd basically be starting from scratch, with just a handful of basic information to go off. Mind reading machines would require recalibration for each species, I don't think magitech would be any different in that regard.
The captured soldiers will likely be insufficient research material to garner a full knowledge. If conventional torture fails, the choice is between
A: throwing magic at them and hope it works and doesn't just outright kill them or do something entirely unexpected. If you're lucky, their mind will be similar enough that if will work regardless.
B: Experimenting on one of the two in an attempt to determine basic structure and thought patterns, then trying to apply what you can gain from one subject to the other and hoping it will work
C: Biding your time and trying to wear them down over the course of many weeks/months in the hopes that they will eventually break or more research material will become available and allow you to gain a more advanced understanding of their minds.
Personally, I'd do C and then experiment on them when you're done. Mind reading tech and magic and all that is brilliant, but may be hampered by limited knowledge. On the other hand, even with limited knowledge there is a long list of basic assumptions you can make about the Septonians and exploit that rather than invade their minds, which certainly carries risk even when done with full knowledge.
Of course, this is all assumption and speculation on my part as to the workings and interactions of magic and the mind, which is really all I can do unless we see it in action
