The Hagen system really does work well but it is limited to smaller tanks. For a while I was running the Hagen system with an additional bottle set up so that the bubble rose into the bottom of the Hagen diffuser. That worked pretty well actually, once I got the hose set up just right.
No the canister is just too small to work any faster. I tried adding extra sugar and it slowed it down a lot. I didn't try adding extra yeast, but it ought to multiply up to whatever working population the bottle can hold fast enough anyhow.
What is your water, pH and KH in the tank before CO2?
Two 2 liter bottles might be good for that size tank, I use a 2 liter on my 20 gallon tank with a Hagen diffuser and on my 29 gallon tank but with a DIY vortex-style reactor. I still have a Hagen running on the 10 gallon, and I am trying to duplicate the yeast and stabilizer ingredients. Still don't know what the stuff is in the stabilizer, but it is mostly baking soda.