@stockey RS DLC are download automatically for both MAC and PC version (p.psarc and m.psarc file) but you only the one corresponding to your OS.
OK let's get back to the basic :
0) You need to OWN Cherub Rock and Rocksmith 2014 Remastered on Steam
1) Delete any d3dx9_42.dll file in Rocksmith root folder.
2) download this : https://drive.google...iew?usp=sharing
3) put it in RS root folder
4) Make sure it's named "D3DX9_42.dll" and exactly that (browser adds "(1)" at the end of file name when you download something multiple times for exemple)
5) Launch Rocksmith via steam (do not use the .exe in Rocksmith folder)
6) You should be good to play any CDLC
7) if it still doesn't work, are you sure you correctly made all those step? If yes we'll need more information because you are probably the 0.000 000 000 001% (aka "no one") of the people for which that doesn't work and without more information on what you did, it's gonna be hard to pinpoint what's going wrong.