The image on that page has:
" - or - upload custom firmware to emonPi2 on ttyAMA0: Browse... emon_CM_6CT_current_only.ino.hex" which is not on my page. I do see that there needs to be “changes to both EmonScripts (v2.3.11) and emoncms core (v11.5.6)”
Clicking on [Full Update] appears to do nothing …[Update Emoncms] does appear to update and after the update completes, the aforementioned line appears 
Clicking on Choose File (formerly Browse...) I traverse to the directory C:\Users\uname\Documents\Arduino\emon_DB_12CT_v1\build\DxCore.megaavr.avrdbopti find the hex file compiled by the Arduino IDE and select it.
The log indicates something to the effect, “first time custom firmware, setting upload, please select the upload again”. I select the upload again. … nothing happens. I click on [Update Firmware] an update occurs, but, in viewing the update log, it looks like the update used is the one on the dropdown box.
I select my file again … nothing happens. I select a previous version that was created by the Arduino IDE and it updates, without clicking on [Update Firmware]. I select my current version and this appears to update, again, without clicking on [Update Firmware].
Now I notice that the display on the emonPi2 is not displaying “emonPi2 starting …” But, it still reboots.
(just documenting my oobe)
Now the powers shown in Inputs are really wrong! Way off. I suspect the the CT calibrations were affected.
At this point I made a fresh SD card, and updated Emoncms.
I modified emon_DB_12CT
changed Set hardware variant to EMONPI2
changed number of voltage channels to 3
changed Link voltage and current sensors
The main feeds, L1 and L2, power are calculated Vn-N times CTn
240V circuits power are caclulated V1-V2 times CTn
120V circuits power are calculated Vn-N times CT depending on the bus (L1 or L2)
change Default calibration values
CT calibrations defaults set to match installation
Enable on-line calibration when running left true
compiled and uploaded it
Back at the inputs page I see that P1 is 3321, P2 is 3312, P8 (EV charger) is 6587. I see -4 on P12 all the rest are 0 to 4. I have to check to see if the 120v circuits on L2 are negative (P10 is on L2)