It sounds like I had a similar experience as you, I'm also 6'4". I had the largest Aeron and it was terrible, especially the hard plastic sides that pressed/cut into my outer thighs. The seat hurt after an hour or two without any real support under, and there was just no configuration that could be done to make any of it comfortable.
I'm not really capable of not-manspreading in order to minimize the Aeron seat side lip pain so one day I brought a belt to the office to tie my legs together so I could relax ... which helped but was just as ridiculous as it sounds. So I just went and bought my own chair instead for my home office and never went back to the office again.
Thanks for mentioning the Titan, it looks like my next chair!
I'm not really capable of not-manspreading in order to minimize the Aeron seat side lip pain so one day I brought a belt to the office to tie my legs together so I could relax ... which helped but was just as ridiculous as it sounds. So I just went and bought my own chair instead for my home office and never went back to the office again.
Thanks for mentioning the Titan, it looks like my next chair!