The below is from their site. You may want to contact them and see if they can increase your limits:
Same as account reloads, players can withdraw as much as they want. For security reasons, the cashier has a maximum amount per request. However, you can always contact Customer Support and request we overwrite our limits so you can submit the amount you want to cashout. Please keep in mind that all withdrawals will undergo an internal review process and any amount larger than 1000 mBTC (1 BTC) may require extra revisions, and that may take from 24-72 hours.