I don't think you can get more buffs if you leave matchmaking where you got your first one or two. On friday I got Magnificence 2.0 and Brilliance 3.2 from playing the Nightfall. Yesterday and today I played the Heroic Strike playlist for 2 hours both days with a Vanguard rep booster active (you get 350+ rep with all the buffs stacking) but didn't get "infected" with any of the other buffs. Seeing as how I got my first two buffs in a thirty minute Nightfall but didn't get more after 4 hours of strikes, I'm convinced you can't get infected anymore if you leave the matchmaking where you first got the viruses. I haven't tried replaying the Nightfall or going into PvP but since the buffs don't stack (according to OP) there's really no point getting all 5, except looking pretty (admit it, even male Titans wearing King's Fall raid gear look pretty with Glitter Head syndrome). Basically if you want all 5 variants of the buff, go into matchmaking (strikes or crucible) on an uninfected character and stay in matchmaking until you get them all.