you would wire both subs togeather to one ohm why couldnt you run both if you could run both dc on one you could run both fis on one if you want to get a 2nd amp you could or stick with one and go bigger
well instead of buying two new dc buy another fi and call it a day and if you want have the old sub reconed so when you play both they will have the same amount of time on then (theres my 2 cents) but what ever you do good luck and post pics
id go with the 9500 series 10's or the 3500 series but the 9500 are bad ass i just bought one of there 9500 18 and its the best sub ive ever owned (and with dd you can get the cones and dust caps to match you truck custom options )