There aren't that many 1600 watt subs amps. I know Audiobahn make ones.

How does your friend's sub sound??

If it kicks hard, then a 1100-1200 watts class d amp should be fine and not too expensive. Like I mentioned above, a JBL BP1200 is an option as well as a DEI 1100d and Memphis ST1000d. I believe Memphis has a 1500 watt amp as well.