the hi-lo converters aren't THAT bad, but they aren't great either....
1800 watts max on a 600watt RMS sub, no way.
I seriously wouldn't worry about it at all. All that matters is the RMS rating. I NEVER look at max ratings, they exist only to spoof people into buying based on marketing hype. Nothing more than a gimmick.
You should be fine with what you have. It should be a pretty nice set-up!