Going 6000cc. I have been told this will require expanders. Can it be done with 800cc saline implants overfilled? (photo)

I hope this is a typo. Saline implants can be over-inflated. The largest volume I have inflated implants to is 2500cc per side. This takes several procedures to reach this volume. I would be very hesitant to go beyond 2500cc.

did you mean 600cc?  The largest implants easily available from FDA approved companies max out in the 900+ cc range, no plastic surgeon would recommend an implant at is 6000cc

I don't think an 800cc implant will tolerate 6000cc of volume. I've never tried though. I know you can take an 800cc implant up to around 1200cc which I have done in reconstruction cases. You are best served to check back with the two surgeons you have met with. I would bet that most plastic surgeons have never put 6000cc into a breast.