I'm assuming that you are running either a KAC-9104D or a KAC-9103D. Both are rated at 500 @ 4 ohms, 900 @ 2 ohms, and 1800 watts max. Both amps are horribly overrated. I've bench tested both amps. Neither would put out more than 644 watts at 2 ohms.
To get a little more output from the subs that you have, I would ditch the kenwood amp altogether. Get an good quality amp that is rated at around 1000 watts at your desired final ohm load. Some good brands to look at are Precision Power, Soundstream, Cadence, JL audio, Sundown, Digital Designs, and RD Audio. All of which will produce their rated power at any load.
Another thing you can do to greatly change the output of a sub system is change the enclosure design.