I have set up clearing deals a few times. You need two things:
1) a broker-dealer and 2) cash deposit for the clearing firm. If you have the deposit (25k-500k depending on the firm) you might be able to hook up with a b/d and piggyback them. After that it's actually quite simple. The truth...
They are a brokerage firm the clears CSS..That means you have to ACAT your account. as far as Great White ( im sorry that was a rock group!) nobody knows anything about them nor why PD would leave clearing firms to join this other one...scary