Can I just run:
H8k's->2x XLR Cables->Phantom Supply-> JB3?
Yes, but no. The signal level won't be very strong and you can only get so much gain from the JB3. You can boost the levels on your computer later, but it's not the same. For a while I ran Superlux SMK-H8K's> XLR cables> ART Phantom II> Audio Technica CP8201 line transformers (see Cheesecadet's post above)> JB3 and still wasn't satisfied with the signal unless it was a really loud show.
FYI - those line transformers definitely add some much needed gain (it's a fixed amount) and they're very affordable ($30), but I quickly discovered that it wasn't enough and moved to the UA-5. Find a stock UA-5 and have it modd'ed by Busman2 (a member here) - I can't recommend that enough!
I've made decent tapes with my Luxes and a couple that are GREAT, but I've got the bug to upgrade - and unforunately no budget to back that up! A few months ago I scored a pair of AT853's from eBay for a reasonable price. I'm VERY pleased with their sound and they're compact enough for unobtrusive (stealth) recording. Stealth use and a variety of capsulesare definitely some things to consider if you haven't already pulled the trigger on the Superluxes. I know there is a hypercard cap for the Superluxes, but they cost almost as much as the entire mic set! For that price you might as well get the Studio Projects C4's....