I'd like to report here the steps I took to achieve success, which took a good half-day so I hope to save other people the time. I'd also like to thank toleda for his incredible work!
1. As explained in toledo's guide on github, download and run MaciASL, add the source https://raw.github.c...njection/master in preferences
2. select new from ACPI -> DSDT, then apply Tools/Patch, first AMI-Clean Compile->Apply, then Enable Audio ID: 1->Apply, Close
3. save the resulting file in ACPI machine language binary (not Disassembled ASL), name it dsdt, copy in a terminal the file into /Extra, so as a result /Extra/dsdt.aml must be present and contain the patched DSDT
4. reboot and run DPCIManager. if the DSDT is ok, you will now have Codec ID = 0x10EC0887 (was blank before)
5. backup and remove /System/Library/Extensions/AppleHDA.kext
6. install AppleHDA.kext from http://www.insanelym...applehda-audio/ - do not use the automated script audio_realtekALC-100_v1.0.4b.command which did not work for me
7. rebuild the kext cache (eg. using myFix) and reboot, then you'll have sound