Fundamentally, there's basically no way you should be able to do what you're trying to do.
The V1 regulator is limited to 2.5A OUTPUT current. It doesn't matter what you shove into it (though it may blow the regulator), the regulator output is limited to 2.5 amps max. A higher input voltage won't change the limit on the output side, other than possibly breaking the unit. Whether the regulator can take a nominal 4.8V input is a Provape question; I haven't seen the specs on it, but that wouldn't change the output range.
If you look at the batteries used in the Provari, they are high capacity, high discharge. The red AW IMR 1600 mAh is rated for 15C max discharge, meaning up to 24 amps. In theory you could then supply over 80 watts into the regulator, but the regulator will never draw anywhere near that power because it is limited to 2.5 amp output, with max output voltage of 6V; you cannot dial higher than 6V, and you're 2.5A limited, so the highest output power you can get to is 15W, and that only at 6V.
If what you want to do, instead, is be able to use lower resistance atties at higher voltages than a V1 Provari, you could have it upgraded to a V2. The V2 trades a little on absolute max power, but increases the max current to 3.5A at lower voltages. Personally I think this is a smart move, since I expect more people are interested at using LR in the lower voltages than care about 6V, but that's just a guess.
See:
http://www.provape.com/v/images/ProVariV1vsV2.pdf The document compares V1 and V2, shows the max amps, and power, at different voltages.