Whew. That doesn't sound like "without too much effort." Don't know if I'll ever be able to play like that but I'm definitely gonna try. Didn't know about cancelling with Drive, though? Gonna look that up...
Its not that hard. All you need to do is getting Swords into enemies (and that one sword attack is very good, where about 10 around him line up and shoot straight simultanously, its a Blitz killer) and then go DT and spam that forward+Triangle move (rapid slash?). That will eliminate any crowd.
Concentration builds fast if you stand still for a moment and do some evades. With full concentration, DT and Triangle+O you'll do Judgment Cut End which is insanely powerful and clears the screen.
As for cancelling, put a sword into an enemy and tap Triangle+O constantly with Force Edge, not too fast, but when the animation hits them. You can stunlock groups to death with this. Also works with Beowulf Kick 13.
With O you can cancel any move or animation. Use that to get out of a combo if you think you'll get hit. I think that with spamming O in general, enemies can't hit you at all.
There is also a just frame Judgment cut which can be performed by holding triangle after any attack and then release it just before the flash happens. Getting the hang of this will also rack up serious damage.