As you already know, since their arrival Lollipop roms require you to flash the a new version of firmware. This is regulary updated with CM12 nightly releases and without it you get bootloops. However, if you use CM11(s) roms and flash the new firmware, your proximity sensor gets broken, resulting in a Screen of Death during calls. Other issues may appear as well. This can be fixed by flashing CM11s modem (contains only NON-HLOS.bin).
When you have your MultiROM up and running, you will need three things: updated CM12 firmware, CM11s modem and the CM12 proximity sensor fix. All files will be attached to this post and regulary updated. So download and transfer them to your device.
Now depending on which rom you are running as primary and which one(s) as secondary/-ies, do the following in one recovery session:
1. flash CM12 firmware from
Install menu in TWRP Recovery
2. flash CM11s modem from
Install menu in TWRP Recovery
3a. if you are running CM12 rom as primary, flash CM12 proximity sensor fix from
Install menu in TWRP Recovery
3b. if you are running CM12 rom(s) as secondary/-ies, flash CM12 proximity sensor fix from
MultiROM menu in TWRP Recovery
4. reboot
*flashable zip contains old blob sensors.msm8974.so, from SlimSaber LP Jan.08.