Why not Just play half the day with everyone using paintball setups and half the day using air soft setups.
Hell you could even work in some storyline to it. Play the morning using conventional human weapons (air soft) with missions based around aquiring new alien technology (paintball guns). In the afternoon the markers your team get to use depends on the mornings performance. Eg. Your team reaches the ancient ruined temple first, you get an a electro pimp gun, other wise, your stuck with a elderly pump gun.
It means we all get a chance to try each others game out, as well as giving giving the paintballers a reasonable handi cap in the afternoon. (The Air soft guys will probably be better at air soft, thus aquire better guns for the afternoon, and so the afternoon does not consist of the paintballers introducing the airsoft guys to a high speed colourful world of pain.)
It does mean you might have to lend your marker to the opposition and maybe even use a site guns, but that's all the more reason to play hard in the morning. And any way wouldn't you like the chance to borrow a decent air soft in the morning.