You'll get levels with or without the preamp. That's, of course, if you are using the levels on the JB3. You'll get the best sound w/ preamp overall. If you are trying to keep it simple, get the latest Denecke AD-20 w/ the 3.5mm input. The battery modle will power the mics, the Denecke AD-20 will amplify the recording and convert analog to digital. Use a Toslink to connect the AD20 to the JB3.
If you are going to get mics that require phantom power, you will need a phantom power module, like the Denecke PS-2, for the mics. Which means, pitch your current battery odule. For Phantom, check my setup below.