Would appreciate suggestions on best way to reinforce floor joists
under a wood floor (I want to support heavy loads, reduce vibration,
make floor as rigid as possible).

Joists are 2x6 on 16" centers, lighter than average 2x8 construction
and could use some help. House is 2 1/2 yrs old.

I've tried some jack posts supporting short extra 4x4 beams across the
underside of several joists. But using posts (in a fairly new and
still-settling house) creates high spots in the floor, requires
contant readjustment. I would prefer strengthening the joist
structure itself if possible.

Thanks in advance to anyone who cares to comment.

Art