If combat styles were simply about math, that would be a solution - simply re-zero the playing field. There is a great deal of flavor in that system, however, and it provides a great framework of mechanics for players to incorporate the stuff they'd like to do.
A relatively quick and dirty solution is to do a spreadsheet of OB/DB for 3 character types: Fighter, Semi-spell user, spell user. Extend that up to 100 levels (or 66, if that's where your critters top out). Add in level bonuses for the creatures: +3 for fighter, cap at +60, +1 for the semi - cap at +20, +0 for the spell user.
Simply refer to that chart, using whatever progression you think is appropriate (and possibly based on the actual party members), and use the level to compare to the creatures in the book. If they're lower than your chart, boost them to it.
One of the companions of old did this, but I gave all my books away a few years back, so I don't have that reference for you anymore.