it would seem to me that if you had the ua-5 gain knobs for ach of your xlr inputs "maxed out" at "4 o'clock" as you state and the levels were still low that you forgot to turn on phantom power to your mics.
the digistatic that you probably experienced was probably the fact that you were running the gain wide open which may introduce tons of broadband noise into your recording. i have found that optimal recording gain settings are right around 1 to 2 "o'clock". in fact i always start at the 1 o'clock and adjust from there as necessary.
when i first started using my ua-5 i would always forget something, phantom power, analog (vs digital), and i still forget to hit stereo (vs mono recording) which is always a bummer. it may be wise to make a "checklist" of how to set up your ua-5 for recording, perhaps on a 3x5 index card that you can laminate and/or tape to the top of the ua-5 to remind you to have all your setting correct.