Not sure why you would need 3x 6.6 in parralell anyway , perhaps diminishing returns ? Looking at the machine it's either an ultra portable with power,or van mount with auxiliary tanks either way I would say auto fill and empty makes sense as options.
That said , I just picked up a Jag cub 1*6.6 motor for hard to get to and small jobs, and I'm keen to try it out as a booster on my airflex turbo , I've got 2x 1400w lamb and a 1500w electro in the turbo so with the 6.6" would give something silly like 420+CFM - perhaps John would hazard a guess? Lift would be average still and I only have 50' of 2" hose ATM so can't give it a good test