Why are you shooting and processing the film at ISO 800 if you want less grain?? There doesn;t seem anything special about the lighting in the scenes that require 800? Isn't shooting at 400 enough? Have you considered even using a slower film if you want even less grain?
You don't - and shouldn't. If you are not blasting your negs to ridiculous levels of overdevelopment (and even then) & have a scanner with competent Dmax, just develop correctly for the grade of paper you normally aim for & they should scan fine - if your basic techniques are ok.
Since I backed down on my development times (developed in pyrocat-hd) for film meant to be scanned, and printed out as digi-negs, the scans better as far as capturing more detail... but it could be my imagination My alt negs for direct printing (carbon transfer especially) are bullet proof and don't fair as well in the scanner... I hope one day you can develop and scan yourself. Control over the process is a wonder thing!