Aaron -- few questions --
1) a ua5 that's not digimodded will only supply a signal to a computer and will not, standing alone, feed a signal to a dat/jb3/etc. Is yours digimodded and/or are you feeding a computer?
2) On mine (digimodded), the phantom power needs to be manually activated each time I turn the unit on -- further, it takes a bit (20 seconds?) after turning on the unit for it to allow me to activate phantom power. Same with yours?
3) assuming the above 2 don't illuminate the issue, do you have another way to provide your mics with phantom power (i.e. a ps2) that you can use to be sure it's merely a phantom power issue (i.e. see if mics>phantom>ua5 will give you a signal)? Another option is to see if the line input on the ua5 provides a signal