Dear
AoxoA, this is Lina from Europe ... I did an extra signup to let you know how brilliant this is!!!
Im running an 24" iMac early 2008 on OSX 10.11.6. The new iTunes version pissed me off instantly, so I just deleted it and replaced everything the OLD way. Which you mentionned didnt work cleanly. I downed to iTunes 10.3 to get this annoying "error -42401", the one you DIDNT come across. Upping step by step to 10.7 didnt make that go away. iTunes worked fine after pressing the error away ... for a few days. Then I noticed a kernel crash while playing songs. Which led me here.
Needless to say I was way too lazy doing ALL the steps since I didnt wanna keep the El Capitan version of iTunes AT ALL.
What I did was everything WITHOUT the steps of iTunes 11 or 12 in your description.
1) turn off csrutil
2) replace iTunes 10.7 installer thingies with Pacifist
3) replace iTunes 10 CoreFP.framework
4) replaced iTunes Library file PLUS the .extras file AND the .xml file
5) restart and BINGO!!!!
iTunes 10.7 is now actualizing my 175 GB Media Library
****** PARTY ***** (and a big fat THANK YOU)