If I get you're post right, here's what you can do. It seems your towers had 2-16 ohm 10's in there. They would have been wired in "parallel" so a receiver saw an 8-ohm load (16-ohms/2=8-ohms). Now you have 2-4 ohm 10's. Just wire 'em up in series and you'l have what you did before, just another way of getting there. (4-ohms + 4-ohms= 8-ohms)