Extracting Acapella with Instrumental (of different volume))

Hi, I'm trying to extract an acapella in Logic using the original track and the instrumental. I know about the method using utility > gain > invert, but for some reason it hasn't been working for me. I believe this may be because the instrumental I have is at a different volume that the instrumental used within the track with vocals.

How do I obtain the acapella track in this scenario?? I assume I'd have to make the instrumentals the same volume, but I'm not sure how to do this to an exact degree. Is there a normalize-like tool to get them at the same levels? Or is there an alternate way to isolate vocals? Sincerely appreciate any suggestions!