well, the good news is:
1. my homemade battery box seems to be working well.
2. the transformers did provide +5 dB gain
the bad news?
1. The transformers suck. They completely trash the signal with what I would call a comb filtering effect, leaving the recording sounding hollow. (I can provide frequency graphs if anyone's curious.)
2. 5 dB gain is not enough.
Granted, these are ratshack parts, so suckage is to be expected. If anyone can help me find higher quality components from someplace like Mouser, I'd try it again. But I believe I need an active preamp for the 4061s.