I’m not sure if this has been suggested yet or not, but what about Vader saying to Luke “Your mother once thought as you do” instead of “Obi-Wan once thought as you do”. I think that would be pretty impactful.
It has, here is a couple of tests people have tried out.
Sir Ridley
https://mega.nz/#!KdkXzIbS!3sc-75YFln-CKefaUOIdNvsNOwRtpAjo9sp7wZycvEc
To mean they never sounded deep enough, I don’t mean in pitch, but like the depth of sound, but I don’t think you can fix that without going back in time and recording James Earl Jones slamming someones mumma.