Hmm.. 4 1ohm coils.. you can have 4 ohm.. 1 ohm.. I think that's it.. 2 for .5 then those two to 1.. all 4 to 4, or 2 to 2, 2 to 2, then that pair to 1..
if you had the two of them, then yeah.. set pairs to .5 ohm.. then series all 4 sets .. .5 + 5 is 1 ohm per sub, then both subs 1 + 1 = 2...